Thinking about my favourite moments, made me think of my least favourite ones too. And seriously, I just needed one of these fav lists I could answer in a sentence (or five):
Act 1, mud mephits. No, just no, they explode, the cover you in mud, they procreate before your eyes. Their tree friends are not much better. Just no. And the worst thing is: Poor Shadowheart is usually out of spell slots by the end so she can't even give the whole gang a bath.
Honourable mentions: The honour mode Shadow-Cursed Shambling Mound in act two, saved from being my most hated by the sole virtue of being optional. The final battle, saved by at least feeling narratively significant.