I agree that the DLC is a little too much of a cheat. I'd rather have had a proper ending than have to wait and buy it later on.
But I thought there was plenty of story going on, the ending is left open so there is plety of speculation to be had, just check out some of the alan wake forums that are about.
As for gameplay, I thought it was quite original. If you don't find it challenging, try playing it on nightmare mode, that'll get your heart racing. As for the bad guys there are several kinds:
Stabby types
Throwy types
Fast moving types
Larger brute types
Chainsaw/Axe wielding types
Birds
Poltergeist objects
Ok so I admit there isn't much in the way of variation, but you can't say there are only two enemies!