It's worth mentioning that Act 2 is probably the most open act in the game, but due to the way this game's level/damage calculations work, you are sort of pigeonholed into a somewhat strict story progression path if you don't know how to majorly cheese stuff. Generally if non-bosses are 2+ levels above you, you aren't supposed to be there yet (as you will inflict less damage against higher level opponents and vice-versa, I think it was something like 15-20% damage per level difference). It might be less of an issue on easy mode though.
