When you were growing up, is there any game that you really just played all the time? Or were you a well-rounded gamer from the day you were born? I didn't have any gaming systems until I got my Game Boy Color when I was 10 or so. I did have an old DOS (and later Windows 95) PC when I was little though, and I remember playing Commander Keen all the time. Then after RollerCoaster Tycoon came out I put more hours into that than I can remember. Those are probably the two games I played more than any in my childhood.
I played Zoo Tycoon and RollerCoaster Tycoon a lot. I played Pokemon Emerald probably the most, I think my playtime was 930 hours? Played Super Smash Bros. Melee a lot as well.
I never exclusively played one game in my childhood. I'd play one game a hell of a lot but I still played other games too. When I was about 5 I played on my parents SNES console a lot just playing some Kirby game. I don't remember which one it was tough, all I remember was button mashing making the little pink blob move. I didn't really know what was going on. Then when I was about 7-8 my parents got a PlayStation for me and my brother for christmas and got us both Gameboys earlier on in the year for our birthdays. From then on I spent pretty much all my time playing either Pokemon Blue or Pokemon Silver (When it came out) on my gameboy or Crash Bandicoot 1/2/3 and Spyro 1/2/3 on the playstation. I also played Medievil but I couldn't play that as much because I always needed my parents help to finish off pretty much all the levels after the Stain Glass Demon fight.
I used to non-stop play PunchOut! and Mario Bros. on the NES with my dad. He was a pro at beating Tyson. I also spent a lot of time playing Super Mario RPG as a kid and the original Pokemon games. :)