Can someone give me a quick tldr why everyone is losing their mind over this?

To keep it very brief:

the setting is awesome, a fantasy world with lots of lore, because it's D&D - there has been a lot of lore written about it, even if not about this particular game necessarily. So people are already familiar with how things work
the company making the game has put out great games in this genre(crpg) with innovative features and engaging gameplay. They have been constantly improving and listening to the community, and don't seem to be one of the companies that are just chasing the next money-making scheme, as they don't support today's P2W or subscription-based models, and even shy away from DLCs, instead opting to give you your money's worth with only one purchase. They also design their games with replayability in mind and with a pretty big scope, so if you like the game you can easily spend hundreds of hours for that $60. Overall pretty good guys
not many d&d games have come out recently (some pathfinder ones have been good contenders though), so this scratches a market itch
the full power of an AAA title for a previously considered nerdy topic. Imagine if comic books suddenly got a 3D movie

I've never played tabletop D&D but I like the idea of it. Is this a game I can just play solo or does it require a party of actual people?
I've played my fair share of PC RPGs (BioWare games, Fallout,...) but never something like this. Is there anything that compares to it? I can imagine it's a slow pace kind of game?
- The two previous games from the same developer - Divinity: Original Sin 1&2 - compares directly to it. Baldur's Gate 3 is essentially Divinity Original Sin 3 (but this time we have the D&D IP rights).
  It's a slower paced game with tactical, turn-based combat.
  Is this a game I can just play solo or does it require a party of actual people?
  There is co-op, but the game works just fine solo.
- I think the only way to play the game is solo as it would be a nightmare trying to coordinate multiplayer for such a long game.
  It’s a turn-based combat game which isn’t for everyone so if you hate those mechanics then this game isn’t for you.
- I’ve played my fair share of PC RPGs (BioWare games, Fallout,…) but never something like this. Is there anything that compares to it? I can imagine it’s a slow pace kind of game?
  Pathfinder Kingmaker & WotR, Solasta, Pillars of Eternity, and Planescape Torment to name a few. Nevermind the fact that BG1 and BG2 are also some of the best ever produced in the genre. Oh, and Larian has their own finger on the landscape with Divinity Original Sin 1 & 2, the games which got them the license.
What is "crpg"? It's the first time I've seen that term
- cRPG (computer role-playing game) is a term that came into prominence to differentiate it from table top role-playing, which was very big in the 80's and 90's. Nowadays it is generally used to refer to old school RPGs of the 90's, or modern games that take after their formulas. Usually the biggest difference between a cRPG and an aRPG (action role-playing game) is that cRPGs are heavily dependent on the character's stats, while aRPGs favour player skill. In most aRPGs you can defeat higher level enemies early on simply through being really skilled. In cRPGs if your character doesn't have the right stats or equipment, then they won't win. That's an incredibly simplistic but accurate difference between the two from a gameplay point of view.
  There are three primary sub-genres of cRPGs. Turn-based (Fallout), real time with pause (Baldur's Gate) and BLOB, which can be either real time (Might & Magic) or turn-based (Wizardry). BLOB, or Blobber RPG, is a first-person cRPG in which you control an entire party through the lens of a single POV. Very small and niche sub-genre that one though.
  Hopefully that helps a little.

It's a sequel (even though in name only, pretty much) to one of the most popular and well-regarded CRPGs of all time, made by a developer with a great track record and lots of public goodwill, uses the incredibly popular official D&D IP, was hyped even before Early Access started in 2020 and has now been in EA for three years.

How is it different from other fantasy RPGs?

I only played like an hour or two yesterday, but the game leans really heavily into the "simulated D&D-campaign" flavour. You have a narrator acting a lot like a DM and you have very prominently displayed (and animated!) dice rolls for loads of actions and skill-checks in dialogues.

Beyond that, wealth of multiple choices and consequences for your actions have been touted as selling points, but I have not played enough to know about any of that.

It's incredibly polished so far, though I still find facial animations (especially eyes) somewhat lacking. But I just played through Cyberpunk and that is a high bar to reach in that specific department.

Alright alright, I've taken the bait. I successfully avoided wanting it until now. I hope you're happy, you just destroyed a lot of my productivity 😭
- It is a really well done game! It’s a bit complex compared to Diablo, more slow paced and super tactical vs. pure hack and slash. I love both!
- To me, video games are never worth 60 dollars. Ever. I usually wait until they are on sale and if they don't go on sale I just never play then.
  I get FOMO for about a week and then it fades away entirely. Most of the time the amazing game everyone is losing their minds over ends up getting massive complaints once the rose colored glasses wear off.

It’s previous entries, Baldur’s Gate 1 & 2 were both epic computer RPGs that more or less redefined the genre on PCs decades ago when they came out (BG1 more so, but BG2 was just as good). For me personally, I sunk countless hours into both those and a few of the offshoot titles that came later (using the same engine I think?).

You have to have played other RPGs at the time before BG1 came out to get an idea of how much simpler they were before. I don’t want to say “bad” because that’s just what the tech allowed for at the time.Then BG1 came out and it was a beautiful painting, it made everything else look like crayon drawings in comparison.

And now along comes Baldur’s Gate 3, decades later and it has some seriously big shoes to fill. It’s been in early access for a few years now I believe, it couldn’t possibly live up to the hype, right? No, it’s good, it’s really good. The full version just launched on Aug 3rd after the developer pulled the launch date up by a month (we normally hear about delays, so an earlier release is somewhat rare). I don’t know that it will have as much relative impact as BG1 had in its day, but it’s a worthy title to carry the name on, something that isn’t always true when we get sequels like this.

The difference between it and other cRPGs is the level of quality in the art/graphics, the faithfulness to the D&D rule set, the amount of freedom/options the game gives you to complete the story, the quality in the writing, and how much the developer listens to the players. It just has a great mixture of all that and they seemed to have knocked it out of the park with this. We’re used to seeing so much subpar shit come out nowadays, it’s refreshing to see a developer who really wants to make something special.

BG2 still holds up (well the remake helps) and still one of the most finest RPG games ever.

It's a well executed CRPG with high graphical fidelity set in a beloved IP. You usually only get two of those three.

It's basically the equivalent of playing tabletop 5e with Larian as the DM.

It's D&D with pretty graphics, your character really feels like he has agenda in the world only after visting few intro camps, party composition can cause some serious story deviations, most of the times if you can think it you can do it...need I to go on?

Actual big and broad RPGs, especially with AAA production, aren't super common. JRPGs are a bit more available, but if you have the itch for different formats, your options are few and far between.

This year is kind of a wild year because there are a bunch of big RPGs in different formats coming out (Diablo 4, Final Fantasy 16, BG3, Starfield), but there are a lot of years with none.

I'm also clueless, and on the Diablo train right now. What is a crpg, how does this compare to Diablo and does it work on the steam deck?

The C in CRPG stands for "computer", and was originally meant to differentiate them from pencil and paper RPGs, like D&D. That is to say they try to mimic what it is like to play D&D style games, with the openness and freedom that entails.
Obviously that is impossible, since in D&D you can do anything you can imagine and describe, provided it fits in the rule framework and the DM plays along. Including, if the DM is willing, just running away from the story to do something else entirely. But CRPGs usually try to let you have multiple ways to solve the problem of the moment.
There's also a big emphasis on story, and very often quests will be delivered narratively. As in, if you wander into a town you might talk to someone who mentions they have a problem and then it's just kind of… up to you to decide how to help? If you'll help? You don't tend to get a marker on your map and a note in your journal to go kill 5 rats, for example.
Also combat is often turn based and you usually control a whole party. So in short it's not like Diablo really.
It does run on steam deck. I had to switch to proton experimental, and the graphics have to be toned down a good bit for 40FPS stable, but because combat is turn based, it won't get you killed. It also handles reasonably well with a controller. It has enough complexity that some stuff takes more than one level of menu to do, and I've made some mistakes due to the differences with their control scheme for Divinity Original Sin 2, but once you get comfortable with it I think it works pretty well.
- Damn I was hoping you'd say it sucked and I could just ignore it...
I wouldn't even compare it to Diablo.
Diablo is like a fun action packed shooter. Like watching John Wick. You're there for the adrenaline.
BG3 is a deep story game with a LOT of choices, a lot of them can go into weird directions. Like watching Lord of the Rings. You're there to seethe a Elf throws the Dwarf.
- Seethe a elf throws the dwarf? Typo, or some kind of reference?

In Diablo side quests do require you to ask how you can help and then you get the marker, so that sounds fairly similar. Is Baldurs Gate a main story and then an endless set of side quests?

Side quests in Diablo and bg3 are vaaaaastly different. They're much more like Skyrim but that still hardly does it justice. In Diablo you find a burning building then the survivor says you need to find her sister in a different unrelated dungeon and you get a nice quest marker directing you there. In bg3 you find a burning building and if you make a skill check you might save the last survivor, then you can extort them for money or just kill them if you really want, then they mention their sister is trapped, you can ignore it or promise help or promise more of a reward, then you get a journal entry describing where you're currently at in that quest and it's up to you how you handle it from there.
- Ok that sounds awesome