Well,...I gotta be honest here. I own FEAR, but have only played MP. I haven't played the SP campaign. I never bothered with FEAR Files because I read all the reviews and they basically said it wasn't worth the trouble.(I usually don't trust reviews very much, but when so many sources say virtually the same thing...you kinda just pass on it.)
All that being said,...this game is truly scary, but for so many different reasons. The lighting is absolutely second to none. The graphics and art direction are the best I have seen...easily as good as Gears 1 and BioShock. The sound set the bar as far as I'm concerned. I simply cannot say enough good things about this game. I would suggest downloading all 5 developer diaries on the XBLM as soon as you can. While watching them you will realize just how much this game was a labor of love for the whole team. They focused so much on the little things. It's the best game I've played this year...better than GTA, NG 2, UT 3, R6V2, and on and on.
Scary game...but you should be more afraid of NOT playing it and missing out!