TDLR It feels as though I am fighting against the game with meta knowledge rather than playing the curated path (with many branches) up to End of act 2.
From Act 1 to end of Act 2 everything felt natural, we went from one thing to another naturally. Having foresight was not necessary to not miss things or feel mislead to feeling false urgency, it felt like having read the book of a movie, I know whats coming but it doesn't ruin my enjoyment of it.
Act 3 feels like its somehow broken and only with my spoiler knowledge that I can correctly navigate. Otherwise I lose things or I am lost. It doesn't help that in Act 3 where there is supposed to be tons and tons of character development and conversation that there are less. Or it feels like its less.
I think Act 3 is great but the rush framing and the ending with the Squid question plot holes just brings everything else down. But there are solutions that don't require a complete rewrite either!
The story-wise essential difference between Act 1-2 and Act 3 is that the story is very linear from Act 1 to 2.
The story in Act 1-2 is essentially like this: you have a logical goal (survive the tadpole infection, understand as "get rid of that thing in my head"). You soon find out the goal is bound to a location called the Baldur's Gate. While there are more than several bridges you may cross, you know where is your destination. Your only decisions to make is which bridges to cross to get to there.
The story in Act 3 is significantly different: You only have a logical goal, but you don't know where to go. Surely, you still have the same logical goal, but the goal is now no longer bound to any specific destination that you know for sure. You feel lost at which bridge or bridges to cross, while there is always a force to push to move forward to cross your next bridge.
From Act 1 to 2, the game holds your hand and meticulously guides you in getting you set on the "right" path to the Baldur's Gate.
Once you have reached Act 3, especially the Lower City, the game won't hold your hand any more. You have to discover your own destiny. Even your goal is only literally the same - its actual meaning has shifted, especially after you have discovered you do NOT have to rid yourself of this infection - it's now understood as "do I have to get rid of that thing in my head or use it for my own benefit?").
Act 3 may have a lot of bugs (loose ends are hard to close after every major change). But it is not nearly as bad as it is occasionally phrased by certain posts online. Without the non-linear nature of Act 3 or the end-game, how may we get up to reportedly 17,000 different endings?
In short:
I like the linear nature of Act 1-2, both in term of story and in terms of adventure.
I like the non-linear nature of Act 3, which means I just have to make own choices then.
I think the "complaints" here are essentially due to some players preferring a more linear story and/or a more guided gameplay.