For me, it has to be Alien: Colonial Marines as it’s terrible due to inconsistent frame rate (moments the game ran smooth and times where lag was insane, even with the best hardware). Both player & enemy AI is crap since the combat wasn’t even that immersive plus Xenomorph AI isn’t as intimidating due to it being poorly implemented.
I beat the demo before getting the actual game, the demo was just levels 1, 2, and 10. When you beat the demo it gives you a code to skip to level 11 in the full version. I ended up beating the game after using the code, but I could never beat level 3, so I never even got to play levels 4 through 9.