After a decade of odd musical diversions, Neil Young came back like a motherf–ker in 1989 with the positively brutal “Rockin’ in the Free World,” which laid waste to most of the heavy metal of the prior decade, as well as most of the punk. “Free World” sounded like it would have been at home on Husker Du’s “Zen Arcade.” Over 20 years later, it still packs a wallop.