I got addicted to Runescape when I was like... 12, haha. It was so bad. I practically stopped sleeping altogether so I could play it more. I had three "online boyfriends" who were each as full of b. s. as I was, lol. And yeah. Then someone hacked my account, stole my gold, chased off my kitten, and finally changed my password.
I was furious at the time, but in retrospect, it was probably a good thing, because I didn't bother starting again.
Well I have a few titles that are my absolute favorite ever - Kingdom Hearts (all of them), Gran Turismo, Crash, Pokemon, . Hack, etc there's a bunch.
But a really detrimental addiction? CoD. I hate this game so much. Everytime I log in I just feel a wave of self-loathing come crashing down on me, but I play all the time. o_o;; Especially Nazi Zombies, cuz it's so mindless and satisfying.