StingingVelvet: The game is completely fine. I enjoy the game. I am hopefully about to finally finish the damn thing. However it is so simplified and so written for a casual audience that I just find myself constantly annoyed it's as successful as it is. I enjoy it but I would take something like Pathfinder: WotR over it without even thinking for a second. So I worry this game will forever change the genre in ways I don't like, as Oblivion did.
Never played Pathfinder: WotR and I couldn't get into Pathfinder: Kingmaker, which seemed greatly inferior to Pillars of Eternity. Granted, I might like it more if I gave it another chance - IIRC, I quit soon after acquiring the kingdom and I never got to be comfortable with the Pathfinder ruleset. I didn't much like the writing up to that point, either.
It may be the case the BG3 mechanics are simpler than Pathfinder but isn't that kind of a given due to DnD5e vs Pathfinder? I'd hardly call DnD5e casual, though. It's still more complicated than many games and so I'm glad BG3 has been much more popular than expected. Hopefully those new to this style like it enough to look at similar types of games in future.
For comparison's sake, how would you rate the mechanics of WotR vs PoE and Dragon Age: Origins? I wouldn't consider any of them mainstream but I wouldn't consider the latter two to be complicated, either. I'd consider DA:O to be significantly simpler than BG3, and PoE to be about on par, although BG3 is partly an immersive sim, which neither PoE or DA:O were, which makes the world seem much more alive.
As for story, I loved the themes, world building and story line in Pillars of Eternity, which was particularly impressive for an original IP but I don't consider BG3's writing to be inferior. I'm only part way through Act 3 but I find the story and dialogue to be well crafted and actually reminds me of a combination of Mass Effect/Dragon Age and the way The Witcher 2 had a lot of threads that came together and I find the reactivity to be mostly good. I think the only baggage BG3 carries vs PoE is the legacy of Faerun, which I don't find as appealing as Eora but it's totally, 100% subjective. The genre certainly has a lot to credit Faerun for, as long running as it has been.
Lastly, I don't worry about any game changing an entire genre for the bad. Whilst it may be a given company no longer makes the games I like anymore, like Bioware's demise and what Obsidian's doing with Avowed, historically it seems independent developers have a way of preserving the greats of the past, regardless.