It's not meant to be a horror movie as such, but more like an critical view of people's reaction to the "Slasher/horror murder torture" film genre, at the beginning of the movie you were told specifically that you had every chance to stop this from happening (By turning off the movie and not watching) the main character of the movie constantly breaks the fourth wall, knowing full well he's playing a role and is using that knowledge to his advantage. He knows you want to see "What happens next" he knows how sympathetic you feel for the family and want to see them live and be victorious, however as soon as things turn around for them (What the Audience wants,,hope expects to happen) he rewinds his version of reality in his favor.
It's not really a horror movie anyway, you don't really see anyone get killed directly, you are shown just a subtle view of the aftermath, only the alternate death scene of one of the killers is shown as an extremely violent event.
During the film, peter is asked by Ann, "Why dont you just kill us", he gives a smile and replies " "You shouldn't forget the importance of entertainment." He's doing all this to please you, the audience. He is just a character in a film playing out his part, and the only reason that the family was killed off in the first place is because you simply refused to stop watching...You killed the family........you sick bastard.