Very good film I don't understand all the negative reviews. It is disturbing for sure. But The accusations of poor acting are rubbish. Its meant to be a found footage film mostly consisting of teenagers on video chat or recording themselves. In that way the actors are very realistic, just like how amateur kids might act on cam.
If you are disappointed because there is no polished and hammy dialogue delivery with OTT expressions and dramatic background music, you should probably stick to watching 'Friends' reruns.
I have a hypothesis. The film is very disturbing, and in the end the villain does not get any sort of comeuppance or anything, so people feel a sense of cognitive dissonance because the bad guy doesnt die in the end, therefore they dont get 'closure' like in typical movies, and just hate the movie instinctivel, and then make up post hoc reasoning for why tthey hated it "Oh the maker is a pervert" or "Oh the script and acting were so bad" LOL.
Anyway, it is quite disturbing and drags a bit in the middle, but on the whole a gripping and well made movie.