It's like Diablo's less attractive, less charming cousin. You pick a character class from six archetypes and commence mass extermination of enemies. You gain levels and find better gear so you can kill stronger monsters, so you can level up and find better gear, so you can…yeah, you know the drill. It's one of those games, where the quest for more progress is paramount, and improving your character isn't just a means to an end but rather is the real goal of the whole operation. Not that there's anything wrong with that, if it's done well.