If you take intense action, hardcore realism, and stuff them into a can of whoop-ass, you get Call of Duty 4.
Ever since I got my hands on the first Call of Duty game, I was aching for developers to create one set in the modern times. Don't get me wrong, the original Call of Duty and Call of Duty 2 were fantastic games (the same can't be said about the third one), but modern warfare games were always something that I gravitated towards.
Both the single- and multi-player modes of Call of Duty 4 are superb and definitely replayable. The realism, ranging from the eclectic selection of weapons to the ability to shoot through walls makes the game all the more immersive. The multiplayer system and all of the things that the developers have done (unlockable items, challenges, perks, etc.) have truly done the game justice. I applaud you, Infinity Ward and Activision.
The graphics are stunning, although it does take quite a bit of power to run this game at a respectable level. When I first saw screens of this game, I was pretty convinced that it was using the new DirectX 10 engine; to my surprise, however, it was still using the DirectX 9 and upping the ante. Boy, it truly had me surprised. I was thrilled that I would not have to spend another $300 to upgrade my graphics card just to experience one of the best games of the year.
If you're more of a single-player person, the campaign does offer a solid eight hours of gameplay, although increasing the difficulty does make certain missions during the storyline difficult at times (which was the intended point). Definitely don't miss out on the multiplayer, though. I was hesitant at first to foray into the online world, but once I did, I was pretty much addicted.
So, FPS fans, what are you waiting for? Lock and load.