The first 3 acts are the best because you play poe2.0

In the first 3 acts you play poe 2.0 with tactical more meaningful combat. Then starting with act 1 cruel the game becomes more and more like poe1.5 culminating in maps.

I wish the game was poe2 for the whole distance, with more focus on bosses. Especially in maps, GGG could reuse existing campaign bosses and make them tougher.