The only MMO I could every really stand was WoW to be honest. I Tried dungeon fighter because' a few friends got me to try it, but really I've played flash games I've enjoyed more =/
The few MMOs out there usually have like, big flat empty areas full of "Level 5 giant rats" that miraculously drop magic cloth pants of forgetfulness.
(Not saying WoW isn't like that, it was just the one I could tolerate)
I think one game I remember that was a free MMO I liked was "Gunz: The Duel". I heard of a sequel to it...I should look that up o.o