If you could pour out action and stuff a box full of it, here's the result. However short it may be.
In CoD4 you play two different characters, one SAS-soldier and one US-soldier, being in different places but involved in the same global crisis. The action is well paced and after a short briefing / tutorial you are thrown on a boat filled with badguys, backed up by your trusted gun and our fellow soldiers. (Who at the start of the game saved my behind more than once I might add)
The friendlies are never in the way and it's intriguing to watch them take up positions before a breach or in a firefight. The action, as I said, is rather scripted and the locations are often filled with obstacles to take cover behind. It's basically just duck and gun from behind cover before you advance to the next critical location. Might not seem like alot of fun when reading, but it is.
You're able to carry two weapons at a time, and you're able to replace them with whatever weapons you happen to find lying around or dropped next to a bad guy or fallen friend. Firing through walls is a useful concept and adds a hint of realism and some extra paranoia when taking cover from enemy fire. Some obstacles are of course able to withstand the barrage of bullets though. The game shuffles some challenging situations with easier ones, but never impossible, making it flow forward at a quite steady pace. It takes a break in the midle of it for a few special missions, one of them I found alot of fun, won't say what it was, but it wasn't like the rest of the game.
Graphicwise it's a beauty, and sound is also very good. The whole story is also quite well written, even if it's rather short. Five or six hours of gameplay, maybe a bit less or more depending on how often you die. The lenght of the singleplayercampaign is actually the only con I find for this game, but if you purchase this game you should really spend hours and hours on the multiplayer, which I assume is alot of fun. (have yet to try it)
In conclusion: Great game, best FPS I've played this year.