Nowadays I totally hate MMOs, but I used to play a few years ago.

Guild Wars has probably been my favorite and actually one of the few MMOs I have played for longer than 2 (intense) weeks, but I have also played EverQuest 2, Lineage II and even what I think is the worst game ever... World of Warcraft.

I'm glad I didn't waste any money on World of Warcraft.

I now sometimes play Air Rivals, but I am not an MMO kind of online player. I want short bursts of intense online play, not long dreaded and very boring grinding.

Its one of many reasons why I prefer to play Day of Defeat: Source and Unreal Tournament III instead.

Also, many of the fantasy MMOs are doing EXACTLY THE SAME THING. It might seem to be structured a little bit differently at first, but basically everyone is copying the Everquest formula.

Another reason why I liked Guild Wars a lot, is also simply because it's free to play. Perhaps I'm just being Dutch about it, but really World of Warcraft is NOT worth paying each month for and from a gameplay perspective this is true for many of the current MMOs.

Some tried interesting things, like SW: Galaxies, but most just fail at being good games to begin with.

City of Heroes.

I played RuneScape for a while till I found WoW...then it all went down hill...lol

I have tried a few MMO games, they mostly turned me off
by their freak interfaces, or boring gameworld.
So WoW was the only game that got me playing for a longer time.
(apart from Browsergames, wich are different in their approach)

Runescape was also too boring, (the version I tested a
free years ago).