Right. Lets get things out in the open here and kept simply.
Campaign - Different spin on the genre. I've always said it would be quite awesome to see the genre go down the Vietnam/Cold War route and it's quite awesome. The use of the Rolling Stones music within some gameplay segments is great.
Multi-player - Currency system. This is great. You get the weapons (to some extent), the perks and the equipment you want, as long as you can afford it. Some weapons need to be unlocked through levelling up, but I can quite honestly say that it's a much better system.
Multi-player - Hardcore free for all. This is awesome. Free for all on CODMW2 was rubbish, as you had to unload, in some cases, a full clip into someone to get them to die. No more with this game.
Multi-player - Lag and glithches. I cannot believe someone said that there is no glitches in the online game. I've managed to notice that whenever someone joins your session, there is a very noticable, yet small, lag in the gameplay. I've also noticed that there seems to be quite a lot of lag in some of the games.
All in all, if you're a hardcore fan of COD, you will enjoy this game. Some people have commented saying that it's just the same stuff that has already been churned out before. Seriously, what did you expect when you bought it if you think that? It's a war FPS. They're technically all the same and barring certain differences, the premise in all war FPS is to shoot the place up in a war type situation.
However, saying that, don't expect to be utterly blown away by it. I really like it, but can't help feeling that in a few weeks time, I'll be picking up CODMW2 again.