-Who the very first Heavy Metal band is (widely believed to be Black Sabbath, as suggested in the film) as well as the roots of metal
-The backgrounds of Heavy Metal musicians and their fans
-Gender and sexuality roles in Metal
-Why a lot of bands have faced problems with censorship due to their lyrical content, album art, and live shows
-Satanic and/or anti-christian beliefs followed by a handful of Norweigian Black Metal bands, as well as other views on religion, satanism, and other controversial topics when associated with metal.
People interviewed include (but are NOT limited to) Tony Iommi of Black Sabbath, Bruce Dickinson of Iron Maiden, Alice Cooper, Lemmy of Motorhead, James "Munky" Shaffer" of Korn, Ronnie James Dio, Corey Taylor and Joey Jordinson of Slipknot, Kerry King and Tom Araya of Slayer, Gaahl of Gorgoroth, Alex Webster and George "Corpsegrinder" Fisher of Cannibal Corpse, and many other metal musicians and producers, as well as multiple fans, socioligists, and even one minister.
The film is a largely independent film with limited theatrical release, so very few are totally familiar with it. A sequal entitled "Global Metal" was released in 2008, which is probably just as good but even less known.