I've been playing Gunz from ijji and I must say it's completely stunning. It has pretty good graphics and the entire game revolves around your use of glitches. Basically, there were some flaws in the development of combat in this game and players have utterly changed the way this game is played over the course of years. Even the GM's need special training from fellow players to keep up with skill levels.
A level 1 can pretty much kill a 90 (though highly unlikly) depending on your abilities. The most basic skill created by players is called "butterfly" which involves blocking and attacking at nearly the same time and many other more involved skills. It can take months to train your finger movements to develop your skills and techniques, but it sure is a lot of fun. It's unlike any other game.
After playing KO for years (and still playing) I find the PvP system in Gunz much better. Although you'll need a lot of effort and patience to get "pro".
I highly suggest playing this game if you're looking for new PvP based games (and a little PvE).