I thoroughly enjoyed Alan Wake, and I am not usually a fan of horror aspect games. I suspect the difference lies within the quality of the scares. Alan Wake doesn't rely on cheap scare tactics, or petty manipulation as so many other games in this genre have in the past. No blind camera angles, no black matt darkness, no unavoidable attacks, and no infinite cloning whilst you have limited ammunition. I think that made it feel both more real, and more fair. Those aspects I have just mentioned never actually scared me they just really frustrated me. Those games ususally just pissed me off rather then actually provided any scare value.
I will say that the game was still too linear for my taste. I would have enjoyed more of a sandbox element. I think the first developer to do a good job of marrying both horror and sandbox will have an instant hit on their hands. You have to admit this about Remedy though based on Alan Wake they are fairly original as the concept and implimentation are concerned. I also wouldn't wager on another four years. They now have an engine under their belt that they are thoroughly versed with. So you can probably cut a couple years out of the development cycle.