Blizzard revealed during Blizzcon that Diablo III amongst other things will contain Team Deathmatch. Two teams of four players each will kill each other as efficiently as possible in ten minutes. Dead players will respawn in three seconds.
Diablo III will also contain achievements. Some of these will be in singleplayer mode, depending on the difficulty level chosen, but achievements will also come in the form of more specific actions, such as killing each boss with your hands only.