Cyberpunk. They fixed most of the issues the game had at launch. There's a dlc coming out soon too that will add a bunch of hours, and with it they are reworking loads of mechanics for free. Can't recommend it enough.
I've reeeaaaally gotten into the rogue-like/lite genre. Dead Cells, Hades, Slay the Spire, FTL, Vampire Survivors... Just endlessly fun and entertaining.
Also for all you Vampires lovers, I just picked up a game called Halls of Torment during the Steam sale for cheap. Super fun "vampires-like"
Witcher 3 wild hunt. Game was released in 2015 and we are still getting regular patches 8 years later. Patch 4.03 was just released last May. Engaging storytelling, a vast open world along with 2 expansion pack, deep role-playing elements to create a memorable and immersive gaming experience.
It's kind of funny because I bounced off the game hard the first two times I played it. What really did it for me was the Ideology DLC, gave it a shot on a whim and the amount of structure it gave me for RPing colonies was exactly what I was missing.
Hundreds upon hundreds of hours in now, and it is the game I keep coming back to. Not to mention one of the biggest modding communities I have ever seen in a video game. The only video game subscriptions I maintain currently are to a few Rimworld modders whose work I really enjoy. When I am not playing it, I am working on ideas of themed mod packs to put into it.
Dyson Sphere Program is a close second, it's my favourite factory-builder. It is still in early access but is a VERY polished experience already. Amazing dev communication too.
Cyberpunk2077 at the moment. Got more than 250 hours on it. Before that I played Dishonored a lot and that before the very first Deus Ex. The story was just incredible and IMHO still is one of the best in video game history.
There's no game I don't eventually get tired of, but here are three that are fantastic and I can recommend playing for hours and hours:
FTL
Slay the Spire
Darkest Dungeon
All indie titles, none of them new, still fantastic and well worth it if you haven't played any on this list. Also all challenging roguelikes, so be warned. =P
I haven't see Horizon Zero Dawn in the comments so far. This is probably the best (by graphics, game play, characters, story lines) game I've ever played. I really hope that Horizon Forbidden West is released for PC soon.
I got Slay the Spire recently from the steam summer sale since it’s so cheap. I haven’t been able to put it down. It’s such a time suck, and I normally don’t even like card games. I would 100% recommend it.
Total: Factorio. Though I do think I need to put that one on hold after I'm finally done with my current save - which is not far out anymore. Also, this game has multiplayer so it may technically not count.
Recent: Derail Valley, a very down-to-basics train simulator, focusing on cargo rail in a fictional rendition of an area in the Balkans. They recently put out a major update, which makes all kinds of simulation features much more expansive.
I'm flabbergasted we're getting no metroidvania love in here so I'll list my two favorites: Hollow Knight and Blasphemous. Both with sequels coming out this year which I'm so excited about!
While they do now have multiplayer modes thanks to their corresponding open source projects, I still think the spirit of these games is firmly in the single player pc game category. Best of all they're both free and available on any OS!
My go to would be Skyrim, but i actually stopped playing about a year ago. My current one would be cyberpunk but i'm waiting for the dlc and playing diablo 4 atm.
Civilization for me... I don't mind the newer versions but I'm old enough that I've played it since Civ I and I do sort of feel like it's lost something as the graphics have improved and animations were introduced.
Still, irrespective of the version, every game is a little different and eats hours like nothing else.
A bit more than once a decade I play them on emulator and try to 100% them. Great fun. I also try to make sure to visit the locations in the real world if I'm on holiday nearby where they based a level.
It's kind of sad that the Venice Beach area hasn't existed since the 90s.
Edit: I did just realise this thread is about PC games, but I do play them on PC albeit through a PlayStation emulator. I do believe the games are available on PC.
Cassette Beasts, it's like Pokémon far more different than other pokeclones, and far higher quality imo. The beast designs are great, and there's a cool fuse mechanic you can use to fuse any two Beasts, with unique art (over 16,000 possible fusions). Also the shiny-equivalent is better done and actually useful.
Edit: Of those that are on PC, anyway. I got tired of waiting for even an announcement that a BB or Demon Souls port was on its way and got a PS5 just for those two things back in January.
Dying Light, absolutely fantastic pakour zombie smasher with one of the best cities in gaming. Bought it originally (on a disc) many years ago and played it so much the disc died and I was inconsolable until Epic gave away the ultimate edition and I was finally able to play The Following DLC.
Now I go and look at Dying Light 2 on Steam and wish my stupid country wasn't so damn expensive, even on sale at 50% off it still costs almost as much as a brand new AAA game in the states. Regional pricing my ass, we always get stung so hard for tech down here.
Since nobody has mentioned it, I'll throw in "X4: Foundations". The X series is janky in places but oh so satisfying if you can get past the jank. Build a military empire to take over the galaxy, or maybe a trading empire. Or maybe you want to become an industrialist and build huge stations to print money. You can be a pirate or a salvager or any combination of the above. And there are tons of interesting mods if you get sick of the vanilla game.
Definitely Civilization in general. There’s a lot of other games I like that are completely different, but year after year I come back to the Civilization series. And even though they peaked at Civ5, it’s still one of the few games I’ll preorder as soon as the next one is available.
Crusader Kings, Europe universalis and imperator Rome. I know this is three games but it's the same general idea, as a history fan, this game scratches a very specific itch for me
There's also bannerlord/warband, amazing experience, sorta like ck3 on a micro level
The Sims 2. I’ve played a fair amount of all four Sims games including their mobile editions, and Sims 2 remains my favorite after a near (yeeesh) 20 years.
The modding community is still relatively robust, especially for a game that’s so old and out of the four, I feel like I can enjoy even the basic gameplay as a storyteller in Sims 2 more than in 3 or 4. In Sims 3, the focus was less on playing multiple families, so it had to be modded right out of the gate to get back to its foundation and I never liked the way the sims looked. Sims 4 “feels” a lot more like Sims 2, which a lot of people hated, but its expansion and content packs are a complete joke. It costs like $2K to have everything, and they’re still releasing packs. I know it’s just the state of gaming these days, but it just sucks the fun out of a lot of the game.
Half the fun these days, though, is just getting the game up and running on modern PCs. I installed a new hard drive a few months ago and it took the better part of a weekend to get the game fully installed and running. I do have Ultimate Collection, but the less time I have to spend in that stupid EA app, the better.
I've also recently began playing Spacebourne 2. It's janky and unpolished as fuck, but it's proving really interesting thus far. Considering it's done by a single dude, it's a miracle it even works.
Grand Theft Auto IV. I've always felt it has the most emersive storyline and setting out of them all. Once you get past the janky driving controls it was a hell of a lot of fun.
Ring of Pain. It's a creepy dungeon crawler roguelite.
I don't know why, I've seen everything the game has to offer and somehow I keep coming back to it.
Most of them that I play since I'm not big on multiplayer. Lots of RPGs (Mass Effect Legendary), colony sims (Rimworld), city builders (Banished), and grand strategy games (Stellaris)
It's not really a single single player game, more a set of specific genres: "Ubisoft open world", "Immersive sim" (especially Arkanes), "Bethesda RPG" (Even 76 which ye cna play pretty much solo), "Walking Sim" (a genre I fell in love with this past year)
I love to start a new round of Civ 6 or a create a new city in City Skylines, because i learned so much from my previous mistakes and this time i will create a perfect civ/city... only to make super stupid mistakes nonetheless and fail miserably.
It's still great fun though.
Almost perfect "simple" rts. Nothing terribly complicated about how it works. Really the only thing that keeps me from saying it is perfect is the lack of ability to set rally points for units or select multiple planets to move all the seedlings(units) all at once.
I tend to get bored of games fairly quickly. I'll hop from game to game to game, over and over again, never (rarely) beating a game before moving on to the next. Sometimes I come back to these games I've abandoned and start over, only to repeat the cycle. There's only one game that I keep going back to again and again. The Sims. I do wish there were other competing life sim games that offered a similar amount of content and mod support, but alas, there's nothing out there quite like it yet.
Spelunky (HD/2) is my goto chill game. Put Spotify on and just start going for the hard end. It's a 2D, roguelike platformer about exploring a series of caves, and shouldn't be as addicting as it is.
I have no idea why, but I cant get enough of it. 200 hours in HD, 250 in 2, and I also had it on X360 a while back that didnt track time.
Some of mine have already been said, so I'll bring up Barotrauma as one of mine! Give me some mods for extra content and I'll be able to play for many many hours.
In the category of "bullet-heaven" / vampire survivors I have been putting a lot of time into Bio-Prototype. It has a really amazing upgrade/combination system for your weapons. And it also only costs like $4
Civilization 4: Fall from heaven: Ashes of Erebus. It can be played multiplayer of course, but I almost exclusively play single-player. The lore is fun, the event system can be interesting, the combinations of awesome Civs+Leaders+Religions+Magic really up the replayability. The end game with hundreds of units amongst a large number of factions with hell terrain encroaching makes for a very dynamic endgame.