Of all the MMORPGs I've played, and I'd wager I've played almost all of them, World of Warcraft is the one I've enjoyed most. I like being able to log on and play for only an hour or two, and then log out with the feeling that I actually accomplished something in the game. I think WoW really accomodates the different playstyles people have, unlike a lot of other games in the genre that more or less force one playstyle on you. Plus, I think Blizzard's art and music direction shines in WoW more than it does in any of their other games, and that's saying a lot especially considering this is an MMORPG.
Second to World of Warcraft, I would have to say Asheron's Call is my favorite MMORPG. The game definitely has its share of problems (a perfect example of a game where a playstyle is forced on you; but not only by the game's mechanics, but by your fellow players as well), especially these days, but it's a very unique game that I really can't compare to any other in the genre.
With all of that said, I too think that Diablo 2 is more fun than any MMORPG I've played, but seeing as it isn't an MMORPG, this is hardly the thread for it.
