My first choice is Rainbow 6 Vegas (PC). That was one of the worst games I have ever bought. Maybe it was because it was so short and ended suddenly with "to be continued". Kinda pissed me off. Glad I only paid $10 for it.
I would also have to say Assassin's Creed. It was cool for about the first 2 missions and then it was the same thing over and over again, just like FC2, but worse imo. I played through it once, but will probably never touch it again.