Having spent most of my productive hours last week playing Call of Duty: Modern Warfare 2, I can confidently say that it's a great, if somewhat flawed, game.
The single-player campaign continues the storyline from Call of Duty 4, with our hero, "Soap" MacTavish, now an officer in the top secret Task Force 141. As with the previous Call of Duty games, the player controls multiple characters, including an Army Ranger and Soap's subordinate, "Roach." Without giving too much away, the fighting takes you from Afghanistan to Siberia and all the way back to Washington, D.C. Most of the levels consist of standard first-person shooting, but there are a decent number of new bells and whistles, including a snowmobile chase, breaching and clearing rooms, and calling in airstrikes from a Predator drone.
The campaign clocks in at a lean 6-7 hours, so some players may feel that they're not getting their money's worth of content. Another problem, which has been persistent throughout the Call of Duty franchise, is the rather obvious manner in which enemies are spawned whenever the player crosses an invisible barrier. Especially on higher difficulty settings, the game degenerates into a slow war of attrition as the player advances just far enough to trigger the next batch of enemies, kills them, then advances just far enough to trigger the next group, repeat ad nauseum. If Modern Warfare 2 was judged entirely on its single-player campaign, it would hardly be worth getting excited over.
But there are two more game modes besides the campaign. Special Ops is a collection of 23 short missions with varying objectives. There are more snowmobile chases, a re-imagining of the Pripyat mission from Call of Duty 4, and a mission where one player backs up another with the firepower of an AC-130. Most of the missions can be played solo, though many of the later missions will be quite hard even on lower difficulty settings. Spec Ops mode really comes into its own when played cooperatively, as two players can back each other up and revive their fallen ally.
Modern Warfare 2 also has a multiplayer mode that's essentially the same as the deservedly praised multiplayer from Call of Duty 4. Not much more needs to be said here: if you loved the Call of Duty 4 multiplayer then you'll love the multiplayer here. There are a few new features, such as new air support options, new weapons, and of course plenty of new maps.