I dont have any aspirations to be a games journalist so im not going to bother you with a full in-depth review of this game like some. Instead, im just going to tell you my thoughts after playing a few hours.
For a start, this is the Battlefield gameplay that made the series so popular. Nothing much new, just the tried and tested formula which is great and works well. Graphics look awesome and remind me of Farcry's and the sound is also excellent and makes the guns in COD4 sound like toy guns. Aside from the servers being busy at the moment, the game has run glitch free for me and very smoothly. The game is also very polished.
The game is quite stripped down with only three maps and classes but for around £10, what do you expect. Its a bargain! Im sure they will add a new map or two in the future.
To conclude ill say this: COD4 is an excellent game. Ive spent at lot of time playing it but playing it is like playing Unreal in a war setting. Its fast, streamlined gameplay and small maps make it quite unrealistic. Battlefield makes you feel like your in a war. Youve got people (not AI) flying planes over you, dropping bombs constantly, youve got buildings crumbling around you (frostbite engine), your parachuting from a plane behind enemy lines etc etc.
Just go buy it!