Metal excess is back: exhibit A this month is Blood Mountain, the follow-up to Mastodon’s 2004 breakthrough, Leviathan, which took Herman Melville’s Moby Dick and refashioned it into one hell of a heavy sea chantey. The Atlanta band consists of four guys who look like tattooed auto mechanics, but they sound like they should be wearing capes and spitting fire. Blood Mountain transforms potentially lame self-help bromides about overcoming great obstacles into a sternum-rattling sci-fi journey through a land infested with all manner of beasties, including a cyclops (“Circle Cysquatch”), warrior tree people (“Colony of Birchmen”) and some sort of sleeping giant. Underneath all this medieval blood and thunder are actual tunes brimming with roller-coaster riffing (“Bladecatcher” merits an Air Guitar Hall of Fame nomination), lost-in-the-catacombs dreaminess (“Sleeping Giant”) and blinding shafts of acoustic-powered star shine (“Pendulous Skin”). Melody matters as much as mayhem, and the treacherous tempo shifts are navigated brilliantly by drummer Brann Dailor, who turns “Capillarian Crest” into a giddy chase through a blinding snowstorm. Yes, sometimes more is better.