So, I accidentally picked the second hardest level of the game and now that I'm on the whitehouse stage I'm seriously thinking about restarting it and doing it again at the harder level because in fact I'm convinced it's going to be too short.
I for one think that the game is awesome, they got rid of the annoying forced-melee mode in some of the older games and the visual scenes and story line is amazing. Going building to building in the US is very eerie. It is short though, you run into some scenes that should take forever, like the siege at the hamburger shop for example. Some scenes are just too short.
I think it's a case where they had a certain budget of time and money and ended up focusing a lot on the exterior game play (planes crashing around you etc....) and it caused them to short the missions. I can't comment much on the online play yet.
One thing that sucks, that I had hoped they had fixed by now, is the ability to play the main missions in co-op mode with 2-3 times the enemies or something, It gets old not being able to crack the game open with your buddies because the campaign has so much more to it then the co-op.