Metal: A Headbanger's journey is a must see for any fan of metal. 31 year old Sam Dunn (an anthropologist from Canada) travels the world to attempt to answer the question "Why is Metal so popular?" He goes in depth through the history, subgenres, culture, and other aspects of what makes up the metal scene. If you enjoy this, he also filmed a follow up documentary "Global Metal" which explores different cultures around the globe, and the impact Metal has on them. I've watched both, and I must say, they are extremely interesting, and well made. He managed to get a lot of interviews from some fairly prominent musicians too. Even if you aren't a fan of metal, it could still be an interesting view if you have an hour or two of time to kill.