A post from a couple of days ago on another forum:
On the merits of the single-player alone, I'd be lying if I said I wasn't a bit disappointed. It's a quality game, yes, and when you go beneath the single-player surface there's so much there it's a ridiculous value... still, I was left wanting. I think the biggest problem the game has to combat is the fact that it released just a few short weeks after Bioshock, which really puts it to shame. It also follows Gears of War, which has superb mechanics and is a lot of fun on its own.
I also found certain vehicle segments frustrating instead of entertaining, and I found the sound mix/voice acting a little problematic. I can't blast my TV in the hours I'm playing, but I found that there was a combination of low-talking in the dialogue and music drowning over it.
At a minimum, most levels were at least "good," with the exception of the eighth, which I didn't care for much... and the story was fine... but I think the game as a whole suffered because it was, in that way, sort of Halo 2, Part 2.
All in all, I was entertained, but I wasn't blown away. I think there are other games that do single-player shooting better on the 360....
I think I'd give it a 4/5
....
Clearly it's a "5" package on the whole when you include all the extras and multiplayer.... wonder how this is going to affect the rest of the year. I'm interested in two more shooters (which is unheard of), because Call of Duty looks sooo damn good, and Orange Box is a fantastic value (I have every confidence HL2 won't disappoint me on the level HL1 did). Hope those get some online love.
Definitely doesn't unseat Bioshock as my game of the year, though.