There seems to be 2 divided sets of opinion on this documentary. It mainly comes down to preconceptions regarding the reality of the supernatural. Conformation bias will have some people getting near the end, hearing the oldest brother's recollection of events and concluding 'it was all a big lie from the start' and consider the first ¾ of the documentary a waste of time.
Those people who do believe in the supernatural or have had personal experience with the supernatural will find the first ¾ of the documentary a fascinating account of demonic influence and possession.
There's really no conclusive evidence for either viewpoint as we can only base our opinions on what has been described by the those who were there and the audio recordings that were made. The viewer will decide who they believe is the most trustworthy in their retelling of events. Who they consider trustworthy will most likely be the party who mirrors the viewer's own worldview most closely.