I was deeply enjoying Enslaved until right up near the end, when it goes all Assassin's Creed and shoves you into mobs of bad guys for two hours. And the 'twist' at the end was a gigantic, incongruous, poorly-conceived slap in the face that almost literally had nothing to do with the rest of the game. Imagine if, at the end of Dark Knight, the Joker had revealed he was actually a robot and everything that happened during the course of the film took place in The Matrix. It's that level of jarring and bad. It makes you throw down your controller in confusion and disgust.
What clinches it is how well Enslaved flows in the beginning. The first fifteen minutes are quite literally one of the most mind-blowingly intense gaming experiences I've ever had, and the atmosphere and chemistry throughout the rest of the game is fantastic. And then it takes a flying train to bullshit-ville and everything turns unbelievably bad.