Any time you try to encapsulate a nearly 40-year-old genre in a four-CD boxed set, you're going to end up with some holes. With The Heavy Metal Box, Rhino has done a fair job of mapping metal's 1968-1991 evolution, from the fuzzed-out proto-metal of Blue Cheer's "Summertime Blues" to the '80s British wave led by Judas Priest and Iron Maiden, to the thrashing triumvirate of Anthrax, Sepultura, and Metallica. Unfortunately for genre aficionados, the legends whose tracks Rhino didn't license will likely stand out more. We get a throwaway cut from Spinal Tap (whose metal lampooning also inspired the set's "this goes to 11" box art) and a Dio-era Black Sabbath tune (the awesome "Neon Knights"), but not a single track featuring Ozzy Osbourne. With AC/DC conspicuously absent, Rose Tattoo's "Nice Boys" (which the equally MIA Guns N' Roses also covered) marks the closest thing to an Aussie hard rock contingent. And while the set's 1991 cutoff ignores the entire post-Nirvana era of metal evolution, punch lines like Dokken, Poison, and Cinderella appear to remind us that if Nirvana hadn't arrived to kill metal that year, the music couldn't have evolved as incredibly as it has today.