Right from the introductory shriek and grind of "(515)," you know Slipknot are deadly serious about making a real heavy metal album. Iowa is intimidating in its unforgiving heaviness. Produced to perfection by wunderkind Ross Robinson, it takes the best of Slayer as a starting point. "People = Shit," "The Heretic Anthem," and "New Abortion" are relentless and wholly brutal, but this is no mere thrash. "Disasterpiece" features a weird, hypnotic riff, while "Left Behind" comes across like a duet between Alice in Chains' Layne Staley and Slayer's Tom Araya. The rerecorded "Gently" builds slowly from industrial atmospherics to a punishing explosion of noise. The title track (also old and formerly known as "Killers Are Quiet") is a deeply unsettling heavy-metal "Midnight Rambler." Frontman Corey Taylor claims to have performed it naked and bleeding from self-inflicted wounds, which isn't hard to believe. This masterfully constructed collection is painfully raw and utterly compelling.