Judd Apatow and Jake Kasdan's uneven parody strikes out as often as it nails the cliches of Hollywood music biopics, but veteran character actor John C. Reilly is electrifying as Dewey, who weathers three decades of musical trends and several lifetimes worth of Behind the Music debauchery. Born into Alabama poverty, little Dewey grows up in the shadow of tragedy: At the age of 8, he accidentally bisected his brother with a machete and permanently alienated his father (Raymond J. Barry). No wonder that little white boy takes to the blues as though to the Delta born! At age 14, Dewey (Reilly) introduces the Devil's music to the high-school talent show and is run out of town on a rail, accompanied by his 12-year-old bride, Edith (SNL's Kristen Wiig). After subbing for steamy juke-joint singer Bobby Shad (Craig Robinson) and wowing both the jiving crowd and record company executives L'Chaim, Schmendrick and Mazeltov (Martin Starr, Harold Ramis, Phil Rosenthal) with his rendition of "(Mama) You Got to Love Your Negro Man," Dewey cuts his first platter — "Walk Hard" — for legendary Planet Records and rockets up the charts. Cue the roller coaster of music business success and excess: Close encounters with Elvis (Jack White of the White Stripes) and Buddy Holly (Frankie Muniz), romance with perky, prudish singer Darlene Madison (Jenna Fischer of the U.S. Office), drugs ("you don't want to mess around with this," warns his drummer — SNL's Tim Meadows — and serial tempter), rehab, groupies, metaphor-heavy protest songs a la Dylan, bigamy, divorce, YELLOW SUBMARINE-style acid trips with the squabbling Beatles (the uncredited Jack Black, Paul Rudd, Justin Long, and Jason Schwartzman), Brian Wilson-esque meltdown, cheesy 1970s variety show, and much, much more. When Cox is performing, the movie is firing on all cylinders: The consistently clever pastiches are penned by the high-powered likes of Marshall Crenshaw, folk-rockers Dan Bern and Charlie Wadhams, Candy Butcher Mike Viola, and the legendary Van Dyke Parks, and Reilly is a hell of a performer — he's got the pipes, the moves and a pitch-perfect sense of how much exaggeration is just enough. In fact, his promotional "Cox Across America" concerts were consistently funnier than the film: Apatow and Kasdan's Cox is a hollow vehicle for spoofing social and musical fads and fashions — imagine THIS IS SPINAL TAP's evolution-of-the-band montage played out at feature length. Reilly created a real character on stage, a swaggering sex machine thoroughly invested in his own legend — that Cox could have juiced the film's hit-or-miss nonmusical sequences, too many of which rely on broad, juvenile gags.