Act 2. Cool atmosphere, consistent story and tone, memorable villains and boss fights, impactful decisions.
In Act 1 I liked the druid-goblin war, but other than that it just feels like a bunch of stuff that doesn't fit glued together.
Act 3 feels haphazard like Act 1, and also a bunch of problems about the whole game culminate in it - like your level and power maxing early on and the difficulty being gone. It ruins the whole gravitas of some villain taunting you when you just know you'll probably obliterate them in one or two rounds.