I see why its only 40 bucks...and still not worth the money. Rent it and you'll see my point.
Campaign is just a remake of the first one, so you've been there done that. Exact same as the first halo game except better graphics and with a button that allows you to show the old graphics.
Then you have multiplayer...yea no. All it is is Halo: Reach. No no armor, you have the rank/armor you unlocked in Halo Reach, all there is are a few new maps. So sure this fun for the hardcore halo players. But its not worth buying, go rent it instead. You can beat the story and you'll probably see that Reach's multiplayer is better than this ones and just go back to it to play that.
Went on Gamestop's review...I am sad at the high rating. Don't get me wrong. I loved Halo Reach, Halo 2, Halo CE, Halo 3, loved all the halo games except ODST. First review is some guy saying how the story for CE is amazing and short if you played the first (okay, whats so fun in a short story mode?). Then he goes off on how the new maps are cool and amazing then how the graphics for everything is great.
Funny thing is, why are you paying money for a short story, map pack, different graphics?
Just do yourself a favor and rent it, I'm glad I did.