wow, thanks for making this great thread, reading it took me back.
My first major addiction was the first crash bandicoot on the PS1. Wow...long time ago. From then I had some major relationships with Diablo II and Arcanum, finishing both more times than I can even think about. Honourable mention should go to starcraft and also to dawn of war actually, two great RTS games.
RPGs were always my thing though, and then when I started playing guild wars things just got so bad. Huge addiction, I played for 3 years, sometimes playing litterally all night, sleeping (well, snoozing) through my lessons at school, then logging on as soon as I got home for more. The only thing I think actually helped me stop playing was that I couldn't log on when I got to uni, because my halls connection was filtered, so we couldn't play them. Done with it now, I had a great time with it, but that was my problem, I love playing a game till it's my *****, and MMOs don't really get like that, unless you're weird or korean. Or both maybe...