Call of Duty 4 is an amazing FPS game that has a realistic feel to it while also being incredibly addicting.
Campaign
As a player, you are thrown into battle playing as both the S.A.S and the Marine Corp. The campaign offers detailed event plots and gives an accurate presentation of Modern Guerrilla warfare. Allies also have much characterization, making the game feel immersive. There is much replay value in the campaign, with many difficulty levels.
Multiplayer
One of the best multiplayer games out on any platform, whether its the PS3, PC, or Xbox 360. There are many game types to choose from as well as a well developed ranking system. Many unlockables to unlock as well, which propels you to keep playing.