Player mostly plays as Sgt. Roach in single player. He belongs to Task Force 141 which is small special force group. There belongs three very important protagonist; Cpt. Price from CoD4, Soap from CoD4 and Simon Riley "Ghost". Main enemy is terrorist called Makarov.
One level gives you option to skip it due to the graphical nature of the scenario it portrayed of a massacre of civilians by terrorists.
Game has a new co-op game mode called Special Ops. It has many independent missions which can be played with friends or alone. Every mission has 3 different difficulties, and easiest gives you 1 star and hardest 3 (if you succesfully complete them). When you have enough stars, you get some new missions. There are 23 missions in total and that means there are 69 stars in total.
Most of the missions are somehow related to story (maps, straight scenes with little mix up). Most of the missions are like "kill x amount of people" or "Reach checkpoint", but there are some very nice competitive ones like snowmobile race from story.
There are 2 different modes on multiplayer: Split Screen and Online. Split Screen is local, max. 4 players small games. It is in any other way the same as Online multiplayer. Game has the new Create a Class system from CoD4 and fully new titles and emblems. They can be earned by completing challenges. Game has new killstreak system too, there are over 10 different ones and you can choose 3 of them once. Highest one is nuke, which kills everyone and ends game. There are many maps, and fan favorite is called Terminal. There are some other popular ones like Highrise and Rust. Guns are mostly balanced. There are some overused guns like ACR, UMP-45 and Intervention. Max player amount is now 18 with new Ground War game mode.
MW2 has only two DLCs. First one is called Stimulus package, and it has five MP maps: Crash and Overgrown from CoD4, Bailout, Storm and Salvage. Second one is called Resurgence pack and it has 5 maps called Strike and Vacant from CoD4, Carnival, Trailer Park and Fuel.
MW2 have been rated 94/100 in Metacritic on X360 and PS3. PC have been rated 86/100. Lowest score i found was 80/100 and highest 10/10. IGN commented"For those planning to check out everything Modern Warfare 2 has to offer: online competition, full co-op Spec Ops mode, as well as the campaign. you're looking at a no-brainer purchase".
Map called Favela was deleted for awhile because one painting had some islamic writing on its frames. Map came back about 2 weeks after it, and now the painting has fully black frames.