If you want a real modern day FPS, look no futher.
The Bad: No character customization (MP), single-player's a little on the short side, AI tends to run in front of you a lot.
First off, the plot (tiny spoilers). You play as two (maybe three) characters in the campaign. A member of the SAS, call sign "Soap", and Sgt. Jackson of the Marine Force Recon team. A man named Imran Zakhaev is a leader of an ultranationalist group in Russia. He revolts against the current government and it sends Russia into a civil war. Doing so, Zakhaev forms a pact with a man named Khaled Al-Asad. Al-Asad is the leader of a coup in the Middle East. Together, they form a small axis. The United States, SAS, and Russians will not let this go unpunished, so they take action
The single player plays out like the previous Call of Duty games. You use the traditional duck and cover feature. No 3rd person cover system here. You have a whole assortment of modern high-tech weapons at your disposal. G36C, M4A1, MP5, and Javelin Missile launcher just to name a few. I played the single player on veteran on my first run and it took me a couple of days to complete. But going back and doing it on normal, it only took around five to six hours. Fortunately, you unlock an arcade mode once completing the campaign to add to its replay value. You can look up your score on Xbox Live to see how your score levels up to the rest of the world. The AI tends to run in front of you a lot sometimes. But AI's not always perfect.
The graphics are breath taking. This game has some of the most stunning visuals I've seen on the 360 (I'm not even playing an HD television). The game still uses scripted death animation but then goes into rag doll once the animation is over. The frame rate is almost perfect and I have yet to see any graphical flaws yet.
The musical score is sometimes unnoticeable. Once you hear it though, it's great. Stephen Barton and Harry Gregson-Williams composed the score. It gives the game suspense, desperation and lots of emotion.
The multiplayer is where the game gets addicting. It's a lot like the previous Call of Duty games where as the enemy spawns at the opposite side of the map if you get into theirs. They added a ton of new features to make the multiplayer feel like a campaign in itself. First, you have the Create a Class feature. You can choose what role you want to be, weapons to use, grenades and abilities. Unfortunately, there's no character customization. But the class avatars are done well. Second, you now have what's called Perks. Perks are abilities that you can choose for each custom class. Examples of these abilities are extra ammo, steadier aim, and higher explosive damage, ect. You have 21 perks to choose from but can only pick three for each class. You start out with only a handful of them until you unlock more. Third, there's a ranking system in which you can unlock more equipment and abilities from gaining experience. Last, there's something called Prestige Mode where if you reach max rank (5 star general) you have a choice to start all over again in the ranks. You gain a new icon and go into Prestige Mode level 1. There are 10 Prestige levels. Which means if you're at Prestige Mode level 10, Rank 55, you've reached maximum rank (605 promotions in all). I can't tell you everything that's in the multiplayer, but I can tell you it's a really fun online experience and really addicting.
Call of Duty 4: Modern Warfare's achievements are all solely in the single player. So that means if you don't have Xbox Live, it's still possible to get them all. Some are very hard and some are easy.
Overall, CoD 4: MW is an extremely fun game and captures modern warfare undeniably well. This is a FPS that everyone should have in his or her collection.