Sonic 2 on Sega Genesis. I loved that game and I would watch my sister play growing up as a little kid. I was so pumped to reach the final level on the plane against the boss!
I was just 7 years old and my parents bought me a Commodore 64 (it was 1987). I clearly remember we arrived at home and I begun to play with "Eagle Empire", a videogame where you are a spaceship and you have to kill many eagles to save the world...here you can find a youtube video of this game.
I was 6 when my Dad brought a Super Nintendo at home and I remember my most prefered game was Donkey Kong: King Country its was the first I played
I actually think the first game I ever played was Space Invaders on an old BBC Micro computer with a green monitor. Why do I suddenly feel so old? lol