I've been pretty fortunate not to have played Universal Studios, Charlie's Angels, Darkened Skye, Hunter the Reckoning, or Turok, etc.
I can't say whether they are the worst games on GC or not cause I've not played them, and I sometimes actually like some of the crappy games, so I'm just gonna say what the worst GC game in my collection is.
And that game is:
Harry Potter - Quidditch World Cup.
It's quite a good concept, but the way they pulled off the actual game-playing was quite shite.
The only enjoyable bit is playing seeker, cause you don't have to concentrate on performing stupid bullet-time moves.
In other positions, all you have to do to move is press forward, left and right. And then press dodge, and throw at the appropriate times.
The game isn't the worst on the GC scene, but it's the worst in my collection. And my sister bought it, so it wasn't a total loss on my part.