The story just kinda falls apart in Act 3 because the main antagonist (Elder Brain) is completely missing, you already killed the only antagonist with character depth, gravitas and motivation (Ketheric) and since it's heavily focused on non-linear side content, almost everything you do effectively undermines the urgency of the story in a way that just doesn't make any sense. On top of that, the characters that do play a bigger role are either boring and poorly characterised (Gortash, Orin) or, to put it mildly, very hit or miss (the Emperor).
The ultimate resolution of the plot is also just bad. I knew that we couldn't expect Larian to deliver a story that could live up to RPGs like Dragon Age Origins but it was still disappointing to see that for all of their different "branches" and lovingly crafted companion stories, the game just utterly fails to culminate in anything that is even greater remotely than the sum of its parts (if anything, the inverse is true).
