Similar to a Stephen King novel ... an amazing setup that starts to lose steam halfway through and limps to the finish.
At least for the first few hours.
The trouble with Alan Wake is, even though the combat is reasonably fun, it's also extremely repetitive and the game becomes more and more combat-intensive as you progress through the storyline. And that's to the detriment of the game's atmosphere and storytelling, which is the big calling card for a game like this. The first half gives you plenty of plot hooks to explore and characters to meet, but halfway through, the story becomes stretched very thin as combat fills out entire chapters and oddball level designs break away from the realistic, natural world and become more obviously video game levels. (The bizarre concert stage being the worst offender.)
Basically, the entire second half is the finale, as all the exposition has been done and you're fighting your way toward the end over several hours of uninteresting monster bashing. It just becomes tiresome and you'll probably be racing toward the next lamppost checkpoint and skip combat entirely where possible just to keep the pace moving along. This is where Heavy Rain did a much better job maintaining that level of curiosity and addictive gameplay throughout the entire length of the game. Like a good book, I felt like I was racing toward the end, dying to find out what would happen next. Regardless of the eventual disappointment I had with Heavy Rain's wonky conclusion, at least they never gave up on their primary mission ... great storytelling and characters. Maybe Remedy put more emphasis on combat because they felt gamers wouldn't maintain interest for the entire game on just storytelling -- or they were just trying to pad out the overall length -- but it really dragged down the experience for me.
All in all, I'd give the first half of Alan Wake a 9.0 and the second half a 7.0, so overall an 8.0 will have to do.