I got Alan Wake and all related content for $1.00 on a Humble Weekly Sale, months ago. Overall I really enjoyed the game.
The atmosphere, and mood of the game world is very well done. It's an odd mix of X-Files, Twin Peaks, and Twilight Zone. The only thing that keeps me from really raving about the game is that the combat gets extremely repetitive.
It was a strange experience, because I was so hooked on the story and the atmosphere, that I forced myself to finish it even though I wasn't enjoying the combat. I almost wished I had just put it on the super easy mode to just basically watch it.
I have not tried American Nightmare, but if I do, I might just play it like that.