Very Well Done
I have to say that as someone who is not typically a fan of this type of game, I really enjoy the game-play so far. It feels like a less frantic Left 4 Dead with an actual story line. Although the game play is very linear, they make great use of the lighting, and even give you a heads up when a battle is commencing. I would have liked to see a more versatile aiming mechanic, but I guess if you aim your flashlight at something it is much easier to shoot at if you can see it.
One thing though, stay on course in this linear style game, the physics, although great, can make it easy to slip off of a rock and fall into the abyss, or get stuck on a rock with no hope but suicide (by jumping into the same abyss you managed to not fall into). I mainly blame the controls for this issue. Also they don't tell you but Alan is very out of shape, he can only begin running by ducking/dodging in the direction you are moving, and after a few seconds of fast jogging he becomes fatigued, and looks like he gained weight suddenly.
I have to agree that this game surprised me but is most deserving of a 4 out of 5. It is not that the game is lacking, it is that if everyone gives it a 5 then Remedy will not try to make improvements. I think that the story telling in this game is what keeps it's rating high, had it been a little less linear, I think it would have definitely deserved a 5.
All that said I can't wait for the DLC, I am eager to see what they add to the story, and what content they add. I will try to give more input once I have had more time to play through this story.