Mw2 is a great game and I was madly in need of its predecessor for the story. Recently I bought it and here's my opinion:
i feel that campaign is still very important despite the rise of Xbox Live and PlayStation Network. The Campaign in my eyes is short but sweet with a intriguing story line and a interesting flashback mission to the Soviet Union. Beginnings and the end are superbly written and the actors voices are very suited to the roles. Although i think that the Veteran difficultly is possibly to hard for less able gamers (especially on the Epilogue mission).
After playing and adoring Mw2's multiplayer I was really looking forward to playing CoD 4's but it wasn't as good as I hoped. the maps were nice but some were lacking. Hardly any weapons are available and lobbies are hacked with weird messages coming up on the kill messages. despite this if you get into a good match it can be impossible to stop as its so much fun!
A good game with streaks of excellent. Certainly get if you've played MW2. If you've already got this and want its successor Mw2 click here-Call of Duty: Modern Warfare 2 (Xbox 360)