The best of the Call of Duty series.
You play as Sgt. Soap McTavish for the S.A.S., and Paul Jackson for the U.S.M.C., who are tring to take down 4 terroists. There is some more stuff during the long story, some twists, and some other stuff I won't ruin for you.
The gameplay is what you could call the same, but with the Modern Warfare setting, there are some minor improvements, like, for example, Night Vision, etc. The weapons are also new (Modern Warfare setting). Controls are basically the same from other Call of Duty games, but without the number hotkeys for weapons.
Some of the levels are pretty sweet, like this mission called "All Ghilled Up", where you are in a Ghille suit, and have to snipe enemies, and move quietly. It's very suspensful. and will keep your heart pounding.
Beating the game unlocks Arcade Mode, where you are given a set number of lives and a time-limit to beat the level (or campaign) dependind on the difficulty setting. Killing a number of enemies increases your multiplier, which increases your score, which you get by getting headshots, stringed kills, and killing enemies.
The game's graphics are gorgeous! Enviroments and character models look real, animations look real, stuff like that.
Overall, buy this game now.