Wow, going back into the old days...
Let's see, Ape escape was great, oh and Super Smash Bros. for the N64, Digdug/Galaga/Pacman. I also liked Sonic Adventures for the dreamcast.
And just wondering, there was this game for the Sega Genesis I liked. It was these two alien thingies and you had to keep getting them up to different levels. Anyone know the name? I forget.