I played WoW a lot back in 2007. Even though I'll never play it again, I do have to say that Blizzard did a superb job putting it together. They did so many things so right with it that it's no wonder it's the biggest MMORPG out there. My only two issues with it would be baggage/inventory and travel time. Other than that, it's almost the "perfect" game.
But I still got utterly bored with it after 4 solid, compulsive months with it.