The Best in the Series

It's a very good game. Probably the best in the series. It's modern - no more WW2 weapons and settings. You fight on a ship, at night (they did a very good job of this), sneak behind enemy lines, and the sniper setpiece is just incredible.
To be honest, when I first played this game, I had a sinking feeling that it would be disappointing. The first level is set in a warehouse - it's very bland looking. But that is about the only bland thing about this game - that one room. Once you get out of there, it's 12 hours of pure awesomeness.
The graphics, as it says on the front cover of the packaging, are photo realistic. This is not only for aesthetic effect; multiplayer also gets an added layer of realism as you would need to blend into your surroundings for maximum efficiency. What your enemies cannot see, they cannot hit. And so do you.
The sound takes you in. There is always an ambient sound effect, especially in the single player campaign. You feel the tension as you sneak under the cover of night, a light breeze blowing. Then, as gunfire erupts and bullets fly, you can really feel that you are in it. You can literally hear bullets whiz by, or whether your bullets are hitting flesh, or stone, or metal, or whether a grenade has landed close by. Again, this adds a great layer to multiplayer. It is absolutely essential to listen to your surroundings.
The guns are great, they penetrate walls with differing degrees based on the gun you use. Multiplayer is beyond excellent. It's meta-excellent. It features an RPG-like element of customization and levelling up, but without the boredom. This is a very realistic first person shooter, but not annoyingly so. You won't (usually) die from a couple shots. A headshot is a one hit kill, as usual.
I would have loved this to the point of illegality had it featured destructible environments. It seems weird that I'm painting a small wooden shack with a machine gun and it's still standing afterwards. But hey, that's like asking for chocolate syrup on a chocolate bar.
To put it simply, if Halo 3 is 10/10, Call of Duty 4 is a 51.2/10.