Hmm, I don't know what I would classify as the worst, but among the worst of the worst is Simpsons: Hit & Run.
It was just a horrible horrible clone of GTA but all of the missions (Did I say all of? I mean EVERY SINGLE MISSION) are either ramming a truck/car to make stuff spill out that you have to pick up, or find someone/pieces to something.
Another would be Disney Extreme Skate Adventure, I got it when I was like 12 and after finding out there were only around 7 tricks and all of them were named incorrectly (And all of the missions pretty much consisted of doing lines (no I don't mean cocaine, but that would have made the experience a slight bit less intolerable)) I put it away and took it back to Blockbuster.
Also as I've noticed, people have said Superman 64.
This game was so horrible that I literally laughed pretty much the whole time I played it, I'm not even going to list how many things were wrong with it or it would take a couple of decades.
Age of Empires III.
Now I'm not saying I hate this game, but I was inexplicably disappointed with it.
The graphics were so demanding I figured "Hey at least if the game play sucks the graphics may make up for it,"
alas I was only slightly right, while the graphics are astoundingly beautiful, it's pretty much AoE II with a couple of useless features and has all of the things that made AoE II good removed.
I don't recommend it but I wouldn't tell you I love it.
Also Driv3r and The Getaway... Yeah, just GTA clones + fail x3.
I only listed games I've played, I feel it wouldn't really be my opinion if I judged a game on other people's reviews.