It's not epic or amazing but it's pretty solid. The single player missions lean heavily on stuff fans will already know and be familiar with. There are a few neat twists but it's pretty by-the-numbers. There's a "oh cool" moment for a sequel if it happens - I wont spoil it.
I've spent less time with the multiplayer and after racking up a lot of time in the past few months on MW2 the match-making felt very slow, why exactly I'm not sure (ps3 version). It's a good game, overall.
The scores in the 5-6 range seem low to me, the Alien gameplay alone is pretty sweet. 7-8 seems more reasonable for scores.