When I was in the second grade, the original Pokemon consumed my life. I spent months upon months beating the first game (and quite possibly actually "catching 'em all," though my memory's a bit fuzzy), I was insane enough to wake up at 7:00 AM (or was it 8?) every Saturday morning just to watch the cartoon, a solid 4 or 5 hours earlier than I would ever wake up on a weekend now, and I bought every little bit of Pokemon-related merchandise I could get my grubby little mitts on.
But I'm not sure if that counts, since the entire Pokemon franchise, not entirely unlike crack, was essentially designed to be highly addictive. Regardless, my most recent gaming addiction would probably have to be Chrono Trigger. I've been playing the game for quite a few hours at a time for about a week or two now (currently stuck for the first time...wonderful) and I've been thinking constantly about it. I can't remember the last time I played a single game this rabidly.