not exactly an MMO, and probably will get hacked to death (after I take some time to bypass xtrap kekeke) but...
http://www.microvolts.com/
game reminds me of GunZ: The Duel so much w/ its glitches.
alternatively, you could try
http://www.youtube.com/watch?v=udEAEARD-Fo
which looks fucking amazing, but again not an MMO