I'm always a bit surprised to see how many people cite Diablo 3 as an alternative. WoW and Diablo 3 are completely different games. Sure there is some overlap and it's safe to assume that many WoW fans like the Diablo series and vice versa, but Diablo 3 is not designed to provide the same experience at all. People on WoW forums frequently say they're quitting the game as soon as Diablo 3 comes out, but unless they've played the other games before I expect many of them will end up disappointed (which will likely lead to more forum whining from people who expected Diablo 3 to be WoW 2).