At first, I wasn't going to buy the game due to the crummy reviews. But the heck with the crowd - I love this franchise. I'm currently playing the Marine campaign and enjoying it very much - just like I'd enjoyed the original 1999
AvP.
More later as I progress in the game, but don't let the lukewarm reviews dissuade you - the game is fun. It might not be as refined as a Gears of War or MW2 or whatever, but if you're a fan of the franchise, you'll dig it.
More here about my reaction to the reviews:
Aliens vs Predator: Resist the Lure of the Hive Mind!