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

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.

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.

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?

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?