Just finished it, and it was the most fun I had with a shooter since F.E.A.R!
I really loved it.
While at five hours or so, the game is really short, it is some of the most awesome five hours you could hope for. The action is fast paced, very intense and has more "holy shit" moments than any shooter I've ever played. While nearly every mission is fasted paced, one of my favorites was a beautiful thirty minute stealth sequence, that was heavily scripted, but highly enjoyable.
The heavy scripting allows for some great set pieces, that work out beautifully. CoD4 is a perfect example of how to put together set pieces in a shooter.
I found the only downside to be the friendly A.I., though it wasn't a problem at normal difficulty.
Initially I played at maximum, having read the ridiculous comment that the game was in the mold of Rainbow Six or Ghost Recon. The only thing it has in common with those games is real world weapons, and a storyline involving modern warfare. The gameplay is not at all tactical, and doesn't provide the same freedom of something like Rainbow Six. And playing at a higher level of difficulty isn't a good idea, mainly because the enemy AI gets unrealistically hard, while the friendly AI's mentally handicapped behavior ends most situations in utter frustration.
So I recommend you play at normal difficulty and blast through like you would any other shooter. The game actually feels more inspired by Michael Bay, than Tom Clancy. The storyline is actually quite good, and has a lot of Michael Bay moments... though without the cheese.
While CoD4 adopts most of the mechanics standard among modern shooters, it does innovate in that it allows you to shoot through certain materials. So if you see an enemy taking cover behind a crate or sheet metal, you can take him out. It also has plenty of moments where you are attacked by dogs, which is a little reminiscent of Wolf3D. Except while those dogs were cute, these can really set your heart pumping.
Anyway I've talked enough, on with the screenies. As you can see, CoD4 looks as good as any game released during the past year. What you can't see is that production values are top notch overall.
If I had to give the game a score, I'd give something in the low 90s.
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