Fable 2. I completely agree with everything Yahtzee said in his review. Story is too short for an "epic RPG". The jobs are boring and repetitive. Other "heroes" were generally useless except during contrived final boss fight (the floating rock, not Lucien...I refuse to consider Lucien to be a boss) in which your gun was more effective than magic combos or melee which you had spent the rest of the game using. Side quests were repetitive and never seemed to effect the world. NPC's were stupid, annoying, and easily amused...in fact, the dog was my favorite NPC in the game, because he actually did something to help (finding treasure, however useless), and because I love dogs. I decided to finally beat Twilight Princess around the same time I first played Fable 2, and Twilight Princess was superior in every way (my only problem with TP being that the story did not feel as epic as Ocarina of Time's).
Assasin's Creed: While Parkour simulation was fun, missions were repetitive, and assasinations boiled down to how well you used the counter in combat. Hopefully, these issues are addressed in AC2.
Bioshock: Initial gameplay was great, and first pivotal story point was amazing, but final boss fight felt out of place, and too easy, as long as you had the flame/ice/lighting thrower.
Halo 3: Mediocre story, but well supported online play. Halo 1 was better, mostly because of how it revolutionized the FPS.
Crackdown: Repetition, repetition, repetition, would rather have been playing Spider-Man 2.