Gameplay very fun and addictive. Story is an absolute disaster.
From what I know from the chunk I've played of Diablo 2-3, the game is about heaven vs hell in a fight to banish "prime evils" and save the world.
In this game you're working with the evils to try and stop a new evil who lost the popularity contest in hell.
No idea why our characters are supposed to be working with the bad guys, and the angels are largely absent from this game.