Ok quite simply this game breaks down into 3 parts, and you have to compare it to COD4 as that is its market!
Story - The story mode is not as good as COD4, you can tell that this game has been built on that success and somehow copies it, but you won't sit there in awe of the game as you did before. The game seems a bit more linear with the respawning enemies being a little more obvious. If you walk down an alley where all the enemies are coming from you will most likely find a brick wall! However the hidden enemies and the flame thrower make up for the shortfalls in the story. I think its a shame that they went back and used some of the graphical elements that we previously saw in COD3. And to be honest you need to set the difficulty to high because it seems very easy!
Co-op - This is the single player missions all over again, but I have to say I love it. You either play in competition with the other 3 team mates or you work together. This definitely adds something to the game and makes it a new playing experience.
Multiplayer - This is where the game really excels, This is better than COD4 or maybe I am just bored of playing those maps for a year! This really is much of the same but improved with more options. The dogs are better than the helicopter as a 7 streak bonus as when you kill a dog you get some points for it at least.
Overall this is a great game and I know I will be playing multiplayer on it until the next one comes out, so buy with confidence!