I know I played a lot of games on the computer when I was really young. The first one was either Sim Life or some educational game my parents got me. I played Mario and even Atari games at various friends' houses but it wasn't until Sonic 3D that I feel madly and deeply in love with video games.
Yes, I know, Sonic 3D.
The thing is, I've always been shit at side-scrollers and while I did enjoy a few of my educational games (some were actually really fun and one even featured Luigi and Yoshi exploring the world) they probably don't count as games to most gamers and didn't really fuel the later addiction.
Sonic 3D, on the other hand, was 3D! Something about taking games out of 2D linearity really did it for me and I took to it like a duck to water. While my brother amused himself with side-scrollers that kicked my ass, I swiftly jumped on the 3D bandwagon and became the video-game champion on the household. It was immensely gratifying, especially as I am the older sibling and being one-upped by my obnoxious kid brother was never fun.
I can not even begin to express the obsession I later developed N64 games such as Donkey Kong 64, Mario 64, and above all Ocarina of Time & Majora's Mask.