I believe it's impossible to SPOIL this film, if you think different: don't read this comment!
Well, think of three men systematically torturing a women using many different methods (and both physical and psychical), their intention is all along to go on until she's dead, they what to see how long she lasts and what it takes. There is no (further) plot what so ever. Everything looks totally real and homemade. All this plus a subtle background sound creates a terrible atmosphere in addition to the horrific footage. (As I see there is about 0.5 seconds of questionable material, it involves a sledge hammer and a hand; I think the response from the hand might be unrealistic)
I thought I somewhat used to disturbing films since I watch Cannibal Holocaust, Scrapbook, Aftermath and alike with hardly no problems.
It's hard to rate this film, one should probably first ask oneself the question (like yamaelle does in a comment): am I already a psychopath to watch this? The important things about this film can probably be fully assimilated without watching it; the only thing you will miss is the (eventual) chock. This film will or have already gone to the history of film creation as the creators probably intended.
Is this art? Well, it's hard to tell.
