I'll name FFVIII for relying on one of the worst plot twists in history.

FFXIII for every reason Fynn mentioned.

Hell, Crisis Core same as the above.

KOTOR because all of really had going for it was the plot twist and I saw that coming from the very beginning of the game.

Fallout 3 I'll give a mention as well. The entire game is fairly poorly written. But things like Broken Steel are so badly written and filed with massive potholes that it's hard not to smash my head against the keyboard.