Paranoid was not only Black Sabbath's most popular record, it also stands as one of the greatest and most influential heavy metal albums of all time. Paranoid refined Black Sabbath's signature sound -- crushingly loud, minor-key dirges loosely based on heavy blues-rock -- and applied it to a newly consistent set of songs with utterly memorable riffs, most of which now rank as all-time metal classics. Where the extended, multi-sectioned songs on the debut sometimes felt like aimless jams, their counterparts on Paraniod have been given focus and direction, lending an epic drama to now-standards. The subject matter is unrelentingly, obsessively dark, covering both supernatural/sci-fi horrors and the real-life traumas of death, war, nuclear annihilation, mental illness, drug hallucinations, and narcotic abuse. Yet Sabbath makes it totally convincing, thanks to the crawling, muddled bleakness and bad-trip depression evoked so frighteningly well by their music. Everything adds up to more than the sum of its parts, as though the anxieties behind the music simply demanded that the band achieve catharsis by steamrolling everything in its path, including its own limitations. Monolithic and primally powerful, Paranoid defined the sound and style of heavy metal more than any other record in rock history.