World of Warcraft... It was sucking up my life so I stopped, I have a level 80 Human rogue and a level 80 night elf druid. I'm still tempted to play again, because I had such good friends...
Oh, Combat Arms, I was addicted to that too, it was pretty fantastic. The only con is that I got bored of it in a few weeks. Have you heard about Vindictus? its by Nexon too.
In total I've played the Unreal Tournament series well over one thousand hours. A rough count would be eleven years. The longest continuous play-through was APB (a game that closed down recently--I'm one of the lucky few who managed to play it! ^^) which I played for about 20 hours constantly, and it also aided me in achieving my first all-nighter.