Though revered as thrash legends, Metallica have put their stamp on countless iterations of heavy metal. “Orion", from 1986's Master of Puppets, finds the quartet pushing into instrumental prog, while 2003's “St. Anger” is the sound of burly vets unleashing scuzzy alt-metal. Then there's “Breadfan", a '70s jam from Budgie that proves Metallica are skilled in the art of the cover.