NES: I'd say World Class Track Meet.
N64: I have to say Superman 64.. I played the first level and quit because of it's cheapness.
Gamecube: I haven't played to many bad games for the GCN either but I say it'd have to be Turok. I started playing it with high expectations and quickly got bored
PC: The worst game I've ever played for the PC was NAM. It had bad graphics, rip off music (one of the songs sounds a lot like a very horribly done version of Paint it Black) and no story line other than you kill the enemy.