I went to see this in the cinema, and it was the most balanced view point regarding metal I have seen. I have been into metal for coming on 2 decades and it has taken this long to see something like this. Added weight is given by the documentary maker being not only a Metal Head but a qualified anthropologist. His study of metal culture is broad and he has done well to fit everything into this film, without getting bogged down.
The interviews with many legends (DIO being the best by far), fans and science types all add insight. This backed up with various music segments just blows it wide open. When it finished I wanted to see it again. Now I can because I am buying it.
For fans get this and show your unconverted mates. They may still not like metal but they will understand your view point more.