When you love CoD you're not really looking for anything new, rather something that's tuned to perfection.
When you have such a well-tuned game in the first place, why would you start changing everything. I feel they got it just right this time with a well-rounded, balanced multiplayer. Air support is perfect; deadly enough that you run indoors, but not so deadly that you don't even have a chance to get a rocket off. Support strike packages are also great, and will help the less experienced feel important and able to help their team-mates.
16 new multi-player maps is, in itself, enough to justify the $60 price tag. Sure, the campaign is short-lived, but really, is that why any of us have really played CoD.
Special ops missions and survival mode are fun and challenging and veteran difficulty is back to the true excruciating challenge it was in MW2. I'll get more playable hours out of this than many of the games I own. To me, that's the true measure of what a good game is, something that you want to keep playing over and over that will give you the most value for your hard earned cheddar.
Call of Duty, and Halo, could almost be considered professional sports now, and as such, shouldn't be drastically changed all the time. They've got a good formula that everybody is clearly hooked on and I think I'll be quite content playing this game for tens or hundreds of hours. Move over Batman, you've just been replaced for the foreseeable future as the favourite on my game shelf.