I've played a bunch of MMO's. Some of them were fun for awhile, some annoyed the hell of me, and some were/are fun still.
Annoyed the hell out of me: Any version of EQ, Star Wars: Galaxies, and Final Fantasy XI. In all actuality, I played FFXI for a whole half hour before tossing it in the bin, since it had no return value. EQ.... well.... it's not called Evercrack for no reason, and there were WAY too many idiots roaming the landscape. SW:G has had so many technical difficulties and rollbacks that I'll never even install it on the PC again.
Fun for awhile: Guild Wars. For months, I played Guild Wars religiously, leveling and ascending two characters, a Monk/Elementalist(Fire), and a Warrior/Monk. I enjoyed the game, but saw so many shortfalls, such as the lack of interactivity in it's environment and the silly limit on how many abilities you could use at any one time. I can't even bring myself to reinstall it and the Factions expansion on this newer PC.
Fun Still: World of Warcraft(Live and The Burning Crusade Beta)... I have a Level 60 Human Rogue, and since the most recent content patch, have become a player-killing machine. Sadly, for now, at Level 60 there is not much left to do but try and get better gear. I will admit that the strategizing and cooperation with guildmates/raid-members is a lot of fun to me. I raid 3-4 nights a week when I'm not sick(been sick a LOT lately. :(). When the Burning Crusade expansion leaves Beta and goes live, I will happily rest with the fact that I will know a good bit already about the new content, and will be able to level again. I intend to level from 60 to 70 as quickly as I can, given the needs of sleep, food, and restroom breaks. Once I am there, I will happily rest for a short time then get involved once again in my guild and raids.
Oddly enough, when I was still playing Guild Wars, I was refusing to even TRY World of Warcraft. I thought the idea of PAYING to play, even though I had already forked out the cost of the game itself was absurd. In the end, I could blow the $15 required per month in a half hour at a coin-op arcade. So..... $15 per month honestly goes a long way. Especially when you play the game as much as I do.