I must say, I'm surprised so few peaople have mentioned Star Wars Galaxies (SWG). It used to have a very large playerbase. Actually, no I'm not, the current fanbase is probably 100,000 strong and shrinking. All due to the Combat upgrade (CU) and New Game Enhancements (NGE). I, personally, think they improved the game immensely. It's one of the few MMO's I've seen as good or not grind-tastic (thanks Yahtzee). I only leveled up to 75 out of the possible 90, and that was so I could use most of the RP-acceptable stuff in the game.
Well, I left runescape after about 2 months (so long ago... seems like it never happened), and got bored, so I went to find another MMO...
Pretty much ALL other free MMO's, come to think of it.
WoW is too cartoony for me to take seriously as an MMO, ergo, I did not go past the free trial. For an FPS, cartoony is ok, such as TF2, but 'serious' games where you have the same character forever just doesn't cut it. It makes rp seem like a joke, and PvP like a fight between Bugs Bunny and Elmer Fudd.
And I thought you had to pay for Guild Wars, what's up with that?