I've been playing it, but I'm not massively impressed with it. Don't get me wrong, I think its a good game, but it doesnt strike me as totally amazing.
The AI is pretty good, but the enemy doesnt seem to leave their area - if I jump out from behind a wall and shoot a few of them, then run, the rest don't seem to follow when I withdraw, just stay in the same area instead of chasing me a little deeper through the level. It was annoying to kill a couple of guys, then hide waiting with my shotgun to take more out, just to wait ages for nothing to happen. There have been a few times where they have sneaked up on me and taken me by surprise, which was awesome, its good to see an AI actually using unpredictable tactics. They also use grenades pretty well.
The action itself is good, but I don't like the slow-mo that much, it makes the game feel too easy. See enemy, hit slow-mo, shoot a few guys, run away, wait for slow-mo to recharge, repeat. I'm finding it far more fun when I use the slow-mo as little as possible, the gunfights are fast and furious in real time, and make the game more challenging.
The weapons are excellent, they have a good balance of realism and shootyness, and the three weapons at any time system works well. The aiming mode could be a little more developed (like call of duty) but makes a fair amount of difference to combat.
The atmosphere is good, but hyped somewhat. The creepy parts don't seem too creepy, but they have their moments. I did have to turn down some of the graphical effects to make the game run smoothly on my pc. Maybe the atmosphere is better with the graphics turned up full, I dont know. The little girl who features in all the trailers and artwork is cool, I won't spoil any of the story behind her, but there are some totally awesome moments featuring her, the designers did this part really well.
I haven't finished the game yet, but so far I'm generally quite pleased with it. It's an enjoyable game with a good atmosphere, but has some areas that could have used more work before release. If you are interested try the demo thats floating around the net before you buy.
Christ on a bike, I didn't mean to type this much.......