What act3 lacks in my opinion is an overarching theme. The first two acts have this, the third just doesn't.
Act1 was all about exploration for me. There's lots of exotic places to explore while you're slowly figuring out what to do about the tadpole. You're getting to know your companions, and also exploring the mechanics of the game.
In act2 you have a clear goal to work towards. Going to moonrise, and then killing Ketheric. And so the whole act is driven by that narrative. Everything you do in act2 feels like it has some connection to that main storyline.
Then act 3 begins with an overwhelming amount of questlines converging on that city. It just feels like I'm going down a list checking off plot point after plot point. There is some excellent content in act3, but it doesn't get room to shine because the whole act is too saturated.
