Green Day vocalist-guitarist Billie Joe Armstrong has eclectic musical tastes. He grew up listening to Elvis Presley thanks to his mom; learned how to play Chuck Berry’s “Johnny B. Goode” on the guitar at age eight; and counts himself an enthusiastic fan of Ramones, Van Halen, Bikini Kill, and Hüsker Dü. Although Armstrong and the rest of Green Day—bassist Mike Dirnt and drummer Tré Cool—excel at spring-loaded pop punk, it makes perfect sense that at least some of these more unexpected influences would eventually start creeping into their music. That happened in a big way on the band’s sixth studio album, 2000’s Warning:. “Waiting” is an optimistic song about fresh starts and new beginnings rooted in fresh-faced ’50s rock ’n’ roll; the title track is a ’60s pop-rock gem about (what else?) warnings that’s reminiscent of bands like The Kinks; and the encouraging “Hold On” is a dead ringer for The Beatles, what with its melodic blasts of harmonica, genteel rock guitars, and even-keeled drumming. Accordion and organ even augment the sea shanty-like “Misery,” a cautionary tale about down-on-their-luck characters who make bad decisions. None of these evolutions sound forced or out of place, which speaks to Green Day’s maturation as a band and their chameleonic musical abilities. And if anything, stretching out beyond pop punk made their more aggressive music hit that much harder—and freed up. “Church on Sunday” is a dead ringer for the Ramones, with Armstrong doing his best Joey Ramone impression, while “Deadbeat Holiday” is ragged rock ’n’ roll with an epic guitar solo. Warning:’s approach sounded quite different from other rock bands of the day, although time has proven that Green Day’s willingness to add depth and texture to pop punk was the right decision. The punkish “Minority” even dove into US politics, critiquing the Republican “moral majority” and foreshadowing the more ambitious—and wildly successful—direction the band took on 2004’s American Idiot.