D&D was created as a roleplaying parody of Tolkiens LOTR saga. What made this story so good on a fundamental level? It was based on fantasy but grounded in reality.
All of the great fictional stories ever written no matter how fantastical have this in common. This is immersion. A reader or player needs to believe the story and setting is plausible for them to be "sucked in" or immersed in said story. Otherwise it is just special effects and the human brain naturally disconnects.
The BG 3 story and setting breaks this fundamental rule at every level. The world the game is set is not grounded in reality, it is a pretty looking chess board with stuff plopped on it. Your companions and their fantastical backstories are quite frankly ridiculous. Could I believe these people existed, sure. Could I believe these people just so happened to be in the same predicament, in the same place AND at the same time? No, why? Because my brain is telling me on an unconsious level these characters are there for the sake of the story not because of it. At this point my brain becomes aware of these anomalies and switches off.
The game world, story and character motivations break rule 1. <<<< This is the story and as such is objectively shite. Chess is a good game but I don't get immersed in it. I don't wonder what motivates the queen or if the king is having it off with the rook because they are just pieces on a board for the sake of a game. BG 3 in a nutshell.
I am not saying this to be overly critical.
Spoilers: You kill all the druids at the grove and find Halsin, you tell him you killed his entire family on purpose. He gets mad for a sec and you say "they were being a dick", he says oh that's ok then and carries on waffling a bunch of words. Total disconnect.
At the Gith patrol the Kith'rak discovers his holy mission is standing in front of him. He asks his minion to kill you and says "I am going to report our success our mission is over" then buggers off to magic land. Eh? He may as well have said "you stay here, I am going home". A real Kung Pow moment made me laugh actually.
Two of the many but these stood out as they made me laugh.