The emphasis is on surviving, not on mowing down schloads of enemies with your chainsaw gun (though if you manage to do that, I'm sure you would get more points). Mechanically, the game is exactly the same as the previous Alan Wake. There are new weapons, the most interesting being the crossbow which doesn't require you to use your flashlight first in order to kill with it. The trade-off is that you can only shoot it once before having to reload.
In games that have some sort of survival mode, I usually just try to hole up with my back to the wall somewhere. American Nightmare's was different in that regard though, for two reasons. The first reason is the two step nature of killing a Taken. Flashlight first. Then gun. It's difficult to quickly kill multiple Taken when you can't backpedal, waiting for the flashlight to do its work. The second is that the maps encourage you to explore. They tend to be quite big and have goodies, like ammo or new guns, liberally scattered around, making it sort of like a zombie-adrenaline-fueled scavenger hunt. Which is the best kind.
American Nightmare's survival mode is tense, difficult, and fun. I probably couldn't play it for too long in one sitting (because I'm a sissy and this game stresses me out), but that doesn't mean it won't be worth your time when the game comes out next week.
