I'm no film critic but I honestly believe 20 years from now when this documentary has become the cult hit I'm sure it will be people are going to look at this movie and realize that it does something almost entirely unique in documentaries today - it leaves space for the viewer to make their own mind up.
I watched it (twice) with two different groups of friends and on both occasions each person had a different interpretation of what they had seen. Almost like when you're looking at clouds in the sky and making shapes out of them. Everybody sees something different. Likewise everyone's reaction to this film was different.
Sure, this film contains the usual devices to help create atmosphere and move the story along (music, the way it's cut, etc) but that's kind of a given. What it does do, which is actually incredibly rare, is give the audience that little bit of space they need to bring their own interpretation to it.
If you research reviews for the film you will find a huge range of reactions from outrage that the film even exists to shock at what goes on to gratitude at the people that made the movie for putting it together.
Almost no other film that I know of sparks such a huge range of opinions. It's almost like the film becomes what you bring to it in many ways. Watch it. With friends!