Isn't just an MMO though. Guild Wars wasn't, neither will this be. It'll totally, without a doubt, blow any and every 'MMO' out of the water. No boring 'go kill 10 skeletons' type quests , and you feel like your actions really do impact the world. It's insane they don't ask for a subscrip fee.
I'm on the fence about D3 for now, purely because I don't want to spend a lot of cash on a game that I'll ditch once GW2 is out.
It won't knock WoW off. Every big game is labeled the world of warcraft killer. Rift, Swtor, everything. WoW is still top dog.