Diablo was one of the original sandbox RPGs... you could wander for hours levelling up... levelling up... levelling up... then go multiplayer and bash the hell out of each other.

It's one of the few single-player games that translated nicely to multi, especially with the logical set-up of hot-keys and abilities and the huge tree system for character and weapons upgrades.

Diablo 2 was a loooooong time ago. People have been waiting for 3 almost as long as Duke Nukem Forever...