I think I have the worst game because it hardly even counts as a game. It has no real goal, you don't control a character, you can't beat the game, and you can't lose. I am, of course, talking about Color a Dinosaur for NES.
There are a lot of bad games out there. Vizzed is right to put everything on the site, but that means the bad ones get through. Since each system has had it's fair share of crap, it's hard to choose. But I think the N64 has one game that is worse than all N64 games, which is Superman 64. Why is this game so bad? It has one of the most glitchy, choppy, and frustrating game play I have ever seen in a game, but definitely the worst I have seen in a 64. I am pretty sure they didn't even bother having people test the game by playing it all the way through because there is no way in hell anyone could have played this game and thought "Yeah, that runs smoothly and easily enough". Epic fail on their part.