Truth be told, bands are generally most innovative early in their career -- unless you're talking about Green Day, that is. In 1994, several years after establishing themselves on the Bay Area punk scene, Billie Joe Armstrong, Mike Dirnt and Tre Cool went national with Dookie, a disc that mashed familiar elements into ultra-accessible forms. Subsequent CDs had catchy moments as well, but they weren't particularly original -- and the comfort-food nature of 1997's "Good Riddance (Time of Your Life)," a sincere strum-along ready-made for proms, was hardly a harbinger of more challenging material. Then, in 2004, the thirty-something Greenies unleashed American Idiot, a disc that combined their indisputable knack for hooky melodies and effective riffs with more artistic heft than they'd previously demonstrated. Idiot is so strong, in fact, that nothing is beyond the realm of possibility anymore. A fascinating new concept album by Foghat? Why not? A brilliant platter from Kenny Rogers? You bet! An enjoyable trip into the mind of Celine Dion? Sure thing! Thanks to Green Day, which visits Denver along with Jimmy Eat World, rules about the rock of middle ages have been revised. About time, too.