Incredible game from start to finish.
After Zakhaev's death he is viewed as a martyr by the Russians and a certain Russian called Makarov is after vengeance towards America. After a certain airport attack comes an astonishing turn of events leading to an all-out war on America's home territory. The story always keeps you guessing but with numerous plot twists it can sometimes be hard to keep up with the frantic story.
Special Ops is a very fun change of gameplay from the singleplayer with 3 different difficulties and 23 different challenging levels it's got plenty of replay value for you and a friend, with whom you can play locally or online, but if you're planning to play online it's best you get a microphone to add to the Special Ops experience.
Now, the Multi-Player is the main bulk of the game, with 70 different Levels of XP and 10 stages of Prestige it gives you heaps of reasons to keep playing, with very little to no lag the gameplay is very fluid and fast. Infinity Ward must have worked hard making sure that no-one will be disappointed with the vast array of weapons, perks, equipment and game modes to guarantee that you will find the play style that best suits you.
In conclusion if you get Modern Warfare 2, you will not be disappointed.