Call of Duty has always been a great FPS series. But the series foray into the future from WWII is a great improvement. The game starts you out as 'Soap' McTavish, a new member of an S.A.S. squad and as soon as you finish training you are placed on a ship out in the Bering Sea looking for a nuclear device. After a daring escape from the ship you switch between 'Soap' and Sergeant Paul Jackson between levels, moving from Russia to the Middle East.
The game constantly changes what you are doing. As in one level your helicopter is shot down by a missile. You and the rest of your squad must fight your way to safety. Then the next level you are the gunner of an AC-130 gunship giving the downed squad fire support. Others you are fighting off enemies from a jeep trying to escape an enemy base.Or you are trying to assassinate an Ultranationalist(sp) leader in Prypiat Ukraine. The single player experiance is much deeper than the other games in the series.
Now the Multiplayer. The single is great and all but the real reason you bought this game (especially if you nave Xbox Live) is the Multiplayer. You start out as a rank 1 Private, but as you get kills you gain exp. As soon as you hit level 4 you unlock one of the games best ideas. the 'Create-a-class' mode. In this you are able to outfit 5 different slots with different weapons and perks. You unlock these by getting to higher levels by killing people, completing matches, or by completing challenges. Challenges are things the game tasks you with doing to gain even more exp. Like calling in an UAV 3 times in a single match. Back to the Create-a-Class, Perks are little abilities that you can give your character like longer sprinting abilities or that your character will drop a grenade when he dies. The multiplayer is the deepest I have seen since R6V1.