Filmmaker Sam Dunn identifies himself as an anthropologist and a heavy-metal fan at the outset of this Canadian documentary, and its form follows naturally: organized like a thesis, it traces metal to its roots and surveys its numerous subgenres, yet every chapter seems to show the goofy, long-haired director flashing the devil horns. Metal culture is a giant topic, and Dunn has made an ambitious stab at it, exploring the music's social, religious, and sexual implications. Many rich topics—the homoeroticism of 80s hair bands, Tipper Gore's campaign against satanic lyrics, metal-stoked church burnings in Norway—are considered and then dropped. But would you respect a movie about metal that wasn't excessive? Codirected by Scot McFadyen and Jessica Joy Wise; with Tony Iommi, Lemmy Kilmister, Ronnie James Dio, Alice Cooper, Dee Snider, and DePaul University sociologist Deena Weinstein. 94 min.