PARANOID proved to be Black Sabbath's most focused, consistent, and successful record. Leaving behind the amorphous, extended jams of their debut for focused songs and a more structured sound, Black Sabbath virtually wrote the book on heavy metal with the ominous, unforgettable riffs, thunderous rhythms, and dark themes on this release. There are some up-tempo rockers, the famous title track for one, but for the most part PARANOID oozes along like a bad dream, as on the slinky, creepy opener, "War Pigs," or the lumbering thud of "Iron Man" (which boasts one of the most indelible electric guitar riffs in rock history).