The best game I ever played was "Freedom Fighters" on Xbox. This is by far the most underappreciated games of all time. I keep hoping that they make some kind of sequel on 360 of PS3, but I havent heard anything yet.
The worst game I ever played was "Busy 3D" the playstation. Holy crap, even as a kid, I found this game incredibly unplayable. Super horrible in every aspect, controlled like shit, looked like shit, and I never had any idea of what the hell I was supposed to be doing.