Don't really know, considering that I constantly try to NOT purchase games that get poor reviews. Overall though, I think it would be Donkey Kong 64. Granted, it isn't a REALLY BAD game, but the camera system is so horible that it make it a lot less fun that it could have been. I sincerely hope that the new version rumored to be in development for the Wii will be a lot better. >_>
Speaking of N64 racing games and perhaps I should've mentioned an N64 game in the first place because of my name, let me say this. My father, being a huge fan of Legos, got Lego Racers for the N64. We played it twice...then never touched it again.
While the N64 version of that game was pretty bad, the PC version actually wasn't half bad for a kids game (I played it a lot when I was 10). The main problem was that the car building feature - which was the main draw - was ruined on the N64. Regardless, the PC version is a lot better than a lot of the liscensed crud that we've gotten over the last decade, IMO.