Though hardly the first heavy rock album, Black Sabbath’s 1970 debut was nonetheless the record that established metal as a separate life force—the first one to envision a horror world beyond psychedelic acid boogie. Presented as sections of extended, multi-part medleys, tracks such as “Wasp” and “Warning” still rank with the band’s bluesier moments. But bruisers like the sludge-caked title track and the crushing “The Wizard” and “N.I.B.” come off like nightmares putting hippie dreams thoroughly to rest.