It's very fun -being a metal fan myself- to watch, but from the anthropologist point of view the makers claim to come from, it's pretty shallow. The answers to questions the maker asks himself are pretty obvious from the get go.
It's great that someone made a documentary about heavy metal from an anthropological perspective, but in my opinion it fails to go deep enough. It seems more like an excuse to arrive at conclusions that were on the maker's mind prior to starting the "investigation".
Again, it's fun to watch, but don't expect any real social science to appear.