The angel of death, Malthael, is the force threatening humanity in the new campaign chapter, and the impressive opening cutscene establishes him as a fearsome adversary indeed, showing us why he's called the reaper of souls.
This expansion adds a decent new character class, a great new campaign act, and most significantly, Adventure mode, a devious Blizzard concoction calculated to make Diablo III's existing content more rewarding-and more addictive-than it has been in the past. What motivates the heroes of Sanctuary to battle the forces that threaten humanity? Is it an unwavering desire to do what's right? Or is it a thirst for more power, more riches, and more stuff? Whatever it is, Reaper of Souls has it.