Honestly, I'm not terribly concerned about some abstract number assigned by a "critic" on some website. I may agree with them, I may not... But I'm not going to let some number make my purchasing decisions.
I also think a lot of these reviews are having a hard time judging this game on its own merits. It isn't really a FPS, at least not like Modern Warfare 2, as so much of the game involves stealth and melee.
Plus, if you aren't a fan of the source material, you're missing out on at least half the fun. The high-pitched whine of a motion tracker is enough to set my nerves on edge, even if I'm just hearing it coming from a television in the other room. Having that integrated into a video game that I'm playing seriously heightens the tension. Something that's largely lost on someone who's never really cared for the Aliens movie.