This is a GREAT question man! For me it has to be legend of Zelda or Pokemon on the Gameboy advanced.
A game that I got really addicted to was League of Legends, I would spend the rest of my time after school playing League of Legends that I would sleep at 11 PM just because I wanted to get a higher rank than before, and I would be in front of a computer for 12 hours just playing and playing.
It's kind of embarrassing to say but for me it's World of Warcraft. I really got into maxing my character out. And then I got responsible in my guild, so I had to do a lot of raids and other stuff. I had people relying on me and for some reason I was putting the people in the game ahead of the people I had in real life.