Uh... I swear I wanted to contribute just 2 or 3 games, but as I wrote, I kept remembering one gem after another... oh well... :)
Outer Wilds - So hard to describe, it's an exploration game, but what you're exploring is a star system going supernova, in a wooden spaceship no less. And a strange way of (not) time travel is also involved, which could be the root of the whole game loop.
Axiom Verge - A platformer that is such a labor of love that it hits just the perfect mix of approachability, exploration, story development and that "huh?" factor where right until the end you're not sure what your abilities actually mean - i.e. if you could glitch through walls in the real world, would that imply the real world is a simulation?
Stardew Valley - A somehow utterly satisfying farming simulator in the style of the first Harvest Moon games. Such a nice getaway game - it begins with your avatar quitting their office job and moving to a farm inherited from their grandfather. No taxes, no boss, no stress, just rise with the sun, plant, water, harvest and fix. Change your rhythm with the weather and the seasons, investigate charming little mysteries of a beautiful place.
Broforce - Another platformer, this one a bit more brutal. Far over the top 80s action heroes bring freedom to the world, but whether you play as Robocop, Schwarzenegger, McGyver, Snake Plissken, Ripley or another 50 heroes is almost random and each hero has completely different weapons and skills. Destructible environment and even a large Xenomorph outbreak (how the heck did they get the license or grant?).
Protolife - This one uses such a madly simple recipe for complex gameplay. Seen top-down, you're a robotic loader than can put down dots. That's all. But certain arrangements of dots are guns, long range guns, flame throwers, area denial, missile silos, barriers and so on. You're attacked by insect-like creatures, but instead of building tanks, you have to attack via well-placed guns slowly pushing the swarming enemies back.
Alien Shooter 2 Reloaded - Simple top-down shooter where you're the lone soldier seeking to contain an alien outbreak. Goes for the time-honed recipe of character stat upgrades (speed, health, accuracy) and purchasing weapons and weapon upgrades. The interesting part is the insane hordes you're up against and that all the corpses stay. It's not unusual for entire corridors to turn into flesh hallways of blood and carapaces.
Moons of Madness - I hope this is actually indie, the graphics are near AAA level. It's 50% walking simulator, 50% cosmic horror, set on Mars. You're an astronaut doing maintenance on an outpost, but rather than go for the "freaky alien attack" recipe, reality itself seems to be somehow bending. Cthulhu, is that you?
Lumencraft - Top-down game. You begin as a miner in an underground base. Something really bad happened to humanity and now you're digging underground for metal and for "lumen." To feed the reactor that keeps humanity alive, you have to meet harvesting goals and dig tunnels, but various enemies attack in waves, so you have to spend part of your resources on fortifications and turrets and avoid opening up too many avenues into your bases.
Carrion - 2D platformer-ish. In a secret place, scientists are holding a horrific, tentacled bioweapon locked away, but it escapes. Twist: you are the tentacled bioweapon, slithering through pipes, circumventing security systems and trying to escape from the lab.
Nuclear Blaze - 2D platformer. You're a fireman sent to contain a fire the broke out in some kind of installation in a forest. But one building has a shaft that leads deep underground where a high-end containment facility is suffering a failure. Takes place in the "SCP" universe and your only tool is a fire hose. Extremely fun trying to extinguish fires in a way where they won't spread again.
Mothergunship - This is a first-person shooter where you're bording and destroying (from the inside out) an army of AI space ships. But instead of a traditional gun, you have gun parts you can stick together. How about a triple rocket launcher with two shotguns in the middle? Or a shield generating laser with a sawblade attache to it, and maybe two shotguns just to be sure? It doesn't grow old with new weapon parts being introduced right until the very end.
Space Run - 2D base building. You're a mercenary cargo pilot fending off space pirates. But you don't do it by controlling a turret, instead, your spaceship is a building surface and you have to build the right kind of engines, turrets, shields and power generators (in mid-flight no less) to be able to shoot down incoming rocks and pirate ships. Extremely well balanced and fun.
Creeper World - 3D real-time strategy. But your enemy is not actually present on the map, you're just fighting a simulation of liquid, a gooey slime that pours out of several spots. You have to keep shooting, bombarding and containing the splashing, pouring slime until you can neutralize the slime outlets. The story is cool, too. The slime is actually some extinct species "gift" to the universe which dissolves everything into data, transmitted to some eternal storage space at the center of the universe.
Shovel Knight - Growing up on games like Mega Man and Duck Tales, Shovel Knight feels like it was made specifically for me.
Celeste - One of my favorite gaming experiences. Great story, great gameplay, and hard as fuck. Incredible accessibility options also.
Recettear: An Item Shop - I don't know anyone else who has played this game but it's so damn good. I love it.
Stardew Valley - The way ConcernedApe continues to add free content to this game makes this easily one of the best values in gaming, but this game would still be great even if content updates had stopped a long time ago. Have to play on PC though for mods; the default walking speed makes the game unplayable for me.
I also put years into a now-defunct multi-user-dungeon called Arythia, but that's kind of it's own whole thing so I don't think that counts.
edit: I can't believe I forgot to include Hades, which is literally one of my all-time favorite games.
Slay the Spire: I don’t just think it’s the best deck building roguelike, I think it’s the quintessential deck building roguelike. It’s such a complete exploration of the design space of the genre in terms of the options it gives the player to build their deck and the challenges it puts those decks up against. Not that there aren’t any other fun games in this genre, but they all still feel like STS, but worse and with a gimmick that doesn’t add much.
Obligatory Undertale mention. I know it's the cliché answer, and it's fan base is...a lot, but it really is a great game.
Also, very happy to see FLT FTL get a couple of mentions here. Hardly any of my IRL friends have even heard of it, but it's probably the best Star Trek game ever made (even if it's not actually a Star Trek game).
It's one of the simplest games possible, the controls are "clockwise" and "counterclockwise", and there are no distracting characters, setting, or story.
And yet the easiest level is -- quite accurately -- labeled as difficulty "Hard". The next 5 levels (6 total) go way up in difficulty (and labelling) from there.
Each level lasts 60 seconds. If you can survive that long. I've never unlocked the final level myself, so I don't even know what it is like, but I can guess.
Outer Wilds and Hollow Knight share the spotlight for greatest games of all time. Both are as close to perfect as it gets.
Bastion gets an honorable mention. Not sure if SuperGiant Games is considered indie anymore, especially now that Hades hit big, but I love their early work.
Lunacid - King's Fieldalike with a great atmosphere and PS1 era esthetic. Fun hidden secrets (sometimes a little too obscure, but whateva, still fun) that I fell in love with as a fan of the OG From Soft King's Field/Eternal Ring games.
Signalis - A thought provoking horror sci-fi game about an android trying to find their missing ship captain on a far away planet. I don't want to stay more to stay away from spoilers, but this plays homage to OG Resident Evil and other early survival horror games from a top down perspective.
Pyre - A sports game and VN hybrid made by Supergiant games. Not as popular (At least I think) as Hades, Transistor, and Bastion. Just fantastic story and world building with characters that you end up feeling so passionately for by the end of the game. Just a wonderful game and probably my favorite Supergiant game barely in front of Hades.
Dusk - A retro FPS ala Quake 1 era games. The game that kicked off the newest resurgence of "Boomer shooters" and is one of the best out there. Wonderful secrets and level design along with some solid atmosphere and scares by those New Blood boys that I love so much.
I feel like people must be tired of me recommending the same few games (you know, if anyone cared enough to read all my comments), but I'm the type of guy who is pretty much only interested in finding the more hidden gems, and I generally ignore the stuff that keeps showing up on the front page of Steam.
The Upturned - A cartoony horror-comedy game with a great sense of humor.
Withering Rooms - The story is interesting and the atmosphere is great.
Your Spider - This one is possibly my favorite indie horror game.
Exanima - Read about the features. This one is more impressive than the screenshots make it look (at least for me).
Lunacid - I love the visual style and atmosphere of this. I also enjoyed Lost in Vivo by the same developer.
Praey for the Gods - This one is for anyone who's looking for more games like Shadow of the Collossus.
8Doors: Arum's Afterlife - This is a decent metroidvania with a charming story. If you enjoyed Hollow Knight, then you may also enjoy this.
Terraria is the easy pick for me. I believe the only game that comes even close to the amount of hours I have in it would be Minecraft. I doubt I need to say much about this game, so I'll leave it at 3 words: near infinite replayability.
Melvor Idle is an amazing game if you like the "idle" in idle games. And if you like the idea of leveling up a multitude of different skills like in RuneScape but don't like the idea of walking back to a town every time you've chopped down 12 trees, Melvor Idle has you covered. It's a long grind but I had fun the whole way. I've 100%'d it and all the DLCs and still love playing it.
Cassette Beasts... I'm genuinely surprised I haven't seen this game mentioned here. An absolutely amazing creature collector with a very unique twist on things, a great story, beautiful pixel art, and hands down the best game soundtrack I've ever heard.
Aside from FTL (which I'm glad to see is well-represented here), my top ones would probably be Papers, Please and Disco Elysium. Papers, Please manages to pair a good narrative leading to many endings with oddly fun gameplay. Disco Elysium simply has some of the best writing ever in a video game and world lore that I can't get enough of.
I also really liked The Binding of Isaac (Rebirth and later), Don't Starve, Shovel Knight, and Hollow Knight.
I’ve really enjoyed playing Tails of Iron (metroidvania with a focus on learning bosses attacks) lately.
For programming games, I really liked Shenzhen IO (You create hardware with something resembling an Assembly language and a printable manual) and Human Resources Machine (drag and drop assembly programming)
I also have a soft spot for anything from Ska Studios (I maed a game with zombies in it, salt and sanctuary, salt and sacrifice, dishwasher, Charlie murder, and a bunch of older games that are probably not playable anymore)
Also looks like everyone else forgot to mention the great game that is Undertale as well.
Tunic. The shortcuts are so cleverly hidden that allows you to easily break the sequence in your next playthrough. The manual translation felt just like back when I tried to understand japanese game manuals that come with game boy cartridges.
Chain of Echoes. A one man RPG game with a unique combat system that has great quality of life.
It's a really well done RPG in the spirit of the original Paper Mario games. Charming and fun to play. Got some depth to the build choices using a similar badge system as Paper Mario or even Hollow Knight.
Against the Storm - I find the loop of those first 30-40 minutes of city building very satisfying.
Ultimate General Series - I love the land battles, it scratches that gun powder Total War itch.
Mount & Blade Series - Playing the Viking Conquest expansion while watching or listening to the Last Kingdom (Saxon Stories) might be one of my favourite gaming memories.
Sea of Stars - Reminds me of Golden Sun. And the soundtrack is just fantastic.
You are in a weird cabin in the middle of the woods playing a card game with your fate on the line. Some of your cards are talking to you and comment on how you play.
Then things get weird.
For those that like Inscryption, honorable mention for Hand of Fate 1 & 2
I played A Short Hike recently, and I was transported. It's a painterly little adventure in which you walk and glide your way through an archipelago, meeting people and solving small puzzles, mostly around platforming. It's amazingly soothing. First game my wife actually enjoys too, and she's not into games at all.
Fight N Rage was my favorite beat'em up before Streets of Rage 4 released, made by mexicans I think, very stylish and manga influenced, tons of juggling and branching paths.
Valdis Story was the hollow knight of it's generation, awesome metroidvania with great bosses and combat with good combos, but it didn't get tiresome like castlevania mirror of fate because regular enemies weren't health sponges, bosses were where you let loose.
Not technically in their bedrooms but made by students - Narbacular Drop. It was the game that spawned Portal. It’s not a great game, per se, but I’ll never forget the paradigm-shifting moment I had when I realized what was happening.
Valve ended up hiring the entire team to work on Portal.
OMORI is incredible. The gameplay is okay (typical JRPG stuff), the music is okay (I've heard better in other games), but the storytelling is some of the best in all of video games, up there with Silent Hill 2 and 3.
The Binding of Isaac is an incredibly addicting game. It's basically rougelike 2D Zelda dungeons, and upgrades stack on top of each other. It's the game that I have the most hours in on Steam (specifically the much better-programmed remake, Rebirth). The DLC is great as well, adding a ton of content. Its replayability is damn near unmatched.
Super Meat Boy is just a really fun, fast paced 2D platformer, that is challenging, but fair. The controls are some of the best of any 2D platformer out there, beating out both Super Mario World and Yoshi's Island IMO.
Battle Brothers: Battle Brothers is a turn based tactical RPG which has you leading a mercenary company in a gritty, low-power, medieval fantasy world. You decide where to go, whom to hire or to fight, what contracts to take and how to train and equip your men in a procedurally generated open world campaign.
The Godfather of Squad-Management-Games!
Songs of Conquest: If you like Turn-Based-Strategy and know HoMM3, you will love this game!
Songs of Conquest is a turn-based strategy game inspired by 90s classics. Lead powerful magicians called Wielders and venture to lands unknown. Wage battle against armies that dare oppose you and hunt for powerful artifacts.
Haven't seen these mentioned, Citizen Sleeper and In Other Waters by Jump Over the Age are incredible games, beautiful artistically and really great world building
Rodina is a very cool space game. You fly a starship - which you can completely design and walk around inside - around an open solar system. You land on planets and asteroids ( seamlessly in real-time) and collect pieces of the very awesome scifi novel-like story. I believe there are now enemy alien bases you enter, but when I played the real draw was the incredible lonely atmosphere of space. It has some of the best newtonian space flight/combat I've played to this day, and the gun play is kind of like old school Doom. I'm sure it's come quite far since I played years ago, but it was literally a one man project at the time.
Graphically, it's very low-poly, and it's not the most varied game, but what's there is 👌
Anyone who likes space scifi should play it. It's incredible, and it came before No Man's Sky released.
Undertale. It was the best game I've ever played and I can never play it again. This game lives rent free in my head, in my fanworks, in the music I listen to and make. It's a game that combines technology and art.
There's a lot I could list here, but I'll focus on a few that I've played recently, that don't seem to be getting as much mention.
Slay The Princess - A literally flawless game. I genuinely mean that. There's not a single thing about this that I can think of to criticise. The writing is fantastic, the art is beautiful, the voice acting is note perfect and the score is gorgeous and haunting. The concept is insanely inventive, and the execution even more so. I finished my first run in about 3 hours, and then looked at what other people were saying about the game and realised that I had only just scratched the surface. As in, other reviews seemed to be describing an almost entirely different game to the one I played, because literally every choice matters.
OTXO - Roguelike Hotline Miami with bullet time and a bartender who sells bottled superpowers. There's really not much more to say than that. The soundtrack is like a Trent Reznor fever dream, and the whole thing has the feeling of encountering Quake for the first time. Just a mad demented bloodrush of insane violence coming at you non-stop.
Vampire Survivors - It's super cheap, it's super chill, it seems like absolutely nothing and then oops its 3am and you're telling yourself you can still get in one more run (no, for real, this game actually fucked with my sleep for a while).
Shadows of Doubt - OK, this one is still early access and I don't actually recommend buying it right now, but absolutely wishlist it for the 1.0 release. It's rough around the edges at the moment, but GOD FUCKING DAMN WHAT A GAME. The sheer audacity of the idea behind this is unbelievable; a fully procedurally generated "city" (about a 3 x 4 block grid on medium size) where every room of every building can be entered and explored, and contains a business or a resident. Every person in the city (up to around a 1000 at the largest sizes) has a complete life; a job in the city that they go to at scheduled hours, places they like to hang out, relationships, maybe a partner, fingerprints, medication for medical conditions, a blood type, a shoe size, height, weight, age... And they do crimes, which you then get to solve for money. You're a PI, in a demented alternate history 1979 ("The Bourbon Empire never fell and now Coca Cola is the President of a retro-cyberpunk dystopia"), down on your luck and taking any job to get by. And when I say "solve crimes" I mean it. This is, IMO, the first game ever to get detective work right. There's no Arkham "Turn on detective vision and walk around until you see all the clues" going on here. You have to actively think about the crime and how to approach it. You can canvass witnesses, dig through government databases, gather prints and match them to a murder weapon, examine the corpse and make inferences about the time of death from which you can pull security footage and look for suspicious characters. You chase down leads, some of which end up as total dead-ends. You have a god damn pin board with string on which to put all your evidence, and then cover it with sticky notes. And it's all you doing this. The game has a tonne of helpful quality of life elements designed to make the process of gathering and assessing evidence as frictionless as possible, but you're the brains. It's on you to actually make the deductions and connections and puzzle out what happened. This game is a work of demented genius and I'm slightly scared of the people who made it.