Just when you thought blues rock couldn’t mutate any further, ZZ Top took a genre known for messy raw emotion and made it something it had never been before: glossy, razor-sharp, and clean. The selections here from ZZ, the Doobies and Ram Jam move like galloping horses made of chrome. They’re complemented by warmer (but still polished) hits like a momentous instrumental from the Allman Brothers, and a warning from Bob Seger about the pitfalls of Hollywood’s siren glow.