It's an amazing game that is worth your time and money.
CoD4 is by far the best shooter on the Xbox 360, and it achieves this high mark by delivering the most amazing action sequences a game of its type has yet to reproduce.
Let alone that it's an incredible good looking and well sounding game. It manages to bridge people who just like to shoot things in a video game to people that are looking for an intense and meaningful storyline that makes you feel as your really making a difference out in the battlefield. I think the reason why this is such a popular game is that it doesn't ask too much from the player, other than a good and steady trigger finger. There are no squad commands for example, and to be honest it doesn't need them because the AI from both sides are pretty good at what there supposed to do, if a grenade is dropped beside one of your allies, they will pick it up and trough it back to the enemy, if there are targets hiding on rooftops or hidden behind windows, they call them out. It's stuff like these that make CoD4 such an outstanding shooter. Missions were you man the fire power of an AC-130 and when you take a long distance sniper shot really take the cake and become missions you want to do more than once. Witch is good, because the single player is a bit on the short side, clocking in at 6-8 hours depending on the difficulty setting you decide to play it on.
I was also very surprised that the guns in the game are incredibly well realized. Not only are you toying with the most powerful hardware available military wise, but the sound, the feel, the minor rumble difference when firing a suppressed gun from a AK 47, to a MP5, to a helicopter minigun, it's all very believable and makes up for some memorable tight fire fights.
And this all comes to full effect in the multy-player mode, where there are over a dozen modes and maps to play around with, and millions of players that are mighty good at the game by now. It's ranking system is like what you may have seen in games like Battlefield 2, where your actions determine what your rewards will be, if you use an ak 47 for long periods of time and get those oh-so satisfying kills, you un-lock scopes, silencers, grenade barrel for that weapon... and that's just some examples, because you can also customize your character with perks, witch is like giving special abilities to your online soldier, you can have it drop a grenade when you die, to pull out your pistol when you die, you can have deeper bullet penetration when fighting people that stay behind walls and some more, sneaky ones, like the one that makes you invisible on the enemies radar. It's all very robust and very polished; chances are that you will fall in love with what the multy-player has to offer and be able to play it for months on end.
All in all, I could spend hours writing about why this is such an amazing game, but in truth, your experience is what matters, go ahead, buy it. It's a game that only gets better the more you play it. It just keeps on giving