Worst Game is a toss up between Rage and Test Drive Unlimited 2. Just couldn't get into Rage, seemed a lot like, drive somewhere, shoot something, turn in a quest, drive somewhere else, shoot something, turn in. Wasn't as fun as Borderlands and didn't even think the graphics were all that amazing.
Test Drive was annoying because it was so buggy. You'd drive stretches of road that the map wouldn't accept you'd driven on, so the sat nav would get confused. Just got a bit samey too.
Let downs included Duke Nukem Forever and (controversially maybe) Forza 4. Duke was funny but a bit old fashioned. I was sorta glad when it was all over to be honest. Forza 4 didn't grip me at all. The career mode didn't really make any sense to me, just didn't get on with it compared to the previous Forza's that I spent a lot of time on.