Actually, to say that heavy-metal music is just a genre of music is almost insulting in some circles. As someone who's too eclectic to really be solely a metal-head, but has been in the realm of the metal world to see how it goes, I can empathize with Sam Dunn's main intention with the documentary; this music should not be seen as just some goofy, crude, offensive, or dangerous off-shoot of old-time rock n roll (not that the last one doesn't apply in one or two cases). It's to show how personal this music, and how this 'way of life' can be for a person, and how it affects personality but not necessarily in the perceived negative light. Dunn, of course, has his head totally together, which is how he can go head-to-head with metal legends &/or notorious sorts like Tony Iommi, Bruce Dickinson, Lemmy, Alice Cooper, Dee Snider, Dio and Rob Zombie (Geddy Lee is also among the big known interviewees, though it's strange to see him here when he's not really 'metal', at least in league with these guys).<br /><br />But through him and his collaborators, he is able to get inside not just the off-shoots and specifics of the world of heavy-metal. The look, the style, the attitude, the controversies both domestic (i.e. Dee Snider's battle with Tipper Gore) and foreign (a superlatively done look at the Norwegian black-metal scene, which is both tense and hilarious), the women bands in the world, and how it helps some people really get better on with life either to hear it or play it or, of course, both. Dunn's look is good if, by necessity perhaps too, too brief, as he at one point lists a kind of heavy-metal family tree of sorts- all too quickly to really see every single one- and barely scratches the surface in the 96 minute running time. Maybe there is only so much that can be covered in a feature-length film, but the subject matter serves to be even more looked into; VH1 had also done a heavy-metal documentary, and it lasted four hours. On the other hand, Dunn and his people actually do get some material here that is more precious, and more enlightening. The juxtaposition of the 'true believers' and horrors in Norways black-death-metal scene with a band like Slayer, who are bad to the bone and have fans who go toe limit, is interesting.<br /><br />It's the kind of documentary that really does work for that it's worth, but not enough of a good thing is explored for fans. Non-fans may get just enough that they can handle, a mix of the basic facts and key points (i.e. the coining of the term 'metal', the roots in the blues, the devil horns, and a look at outrageous album covers). It's good subjective film-making, though edging a little much on trying to get enough history along with the personal history.