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.
During childhood for me it was legend of mana it also the game that keep motivating me to read English dictionary due to how confusing some of the mini quest are and my lack of understanding of baby talk or lisp make me need to puzzling what they are talking to the point somehow I understand English without it.