Combat Arms: Kinda like soldier front and WarRock, it's an online FPS that has ranks/levels and exp 'n shit.
pretty fucking fun, me and my brother own all the time on that game.
http://combatarms.nexon.net/Intro.aspx
MapleStory: It's like a sidescrolling mmorpg, i know it sounds absurd at first, but give it a try, it's pretty fun just going on random adventures and owning cute japanese monsters.