"Walk Hard: The Dewey Cox Story" is a bawdy, rib-tickling, anything-goes spoof of such recent music biopics as 2004's "Ray" and 2005's "Walk the Line," and here's the kicker—it's actually a better movie than both of those. By putting a wickedly clever spin on the clichés permeating throughout the genre, writer-director Jake Kasdan (2002's "Orange County") and co-writer Judd Apatow (2007's "Knocked Up") have reinvigorated the tired conventions and made them new again. Sure, the film is silly and purposefully exaggerated for optimum comedic effect, but the deeply flawed fictional musician of the title, played to the hilt by a career-redefining John C. Reilly (2007's "Year of the Dog"), becomes real enough that his life takes on a sort of heartfelt, albeit twisted, pathos for the viewer.

In 1940s Springberry, Alabama, 8-year-old Dewey Cox (Conner Rayburn) sets out with perfect older brother Nate (Chip Hormess) for a care-free day of rattlesnake throwing and tractor dodging. When Nate happily proclaims that it's a day when "nothing could go wrong," it, of course, does, leaving Nate sliced in half real good at the accidental machete-wielding hands of Dewey. Growing up with childhood memories that haunt him and a bitter father (Raymond J. Barry) who reminds him every chance he gets that the wrong son died, a fed-up 14-year-old Dewey (42-year-old John C. Reilly) finally runs off and marries 12-year-old sweetheart Edith (34-year-old Kristen Wiig), promptly knocks her up with a gaggle of children, and sets upon making his dreams as a musician come true. He hits the jackpot with a successful song called "Walk Hard" that shoots him into superstardom. With fame, however, comes a downward spiral of drugs and crime that not even duet partner and second wife Darlene Madison (Jenna Fischer) is sure she can cure.

Spanning seven decades that take Dewey from an 8-year-old boy to a changed 71-year-old man, "Walk Hard: The Dewey Cox Story" has an epic timeframe and almost an epic feel to mimic the Ray Charles and Johnny Cash biopics from a few years ago. The difference is that this story is played for laughs. A lot of laughs. Though not all the jokes work—an animated LSD trip with The Beatles (played by Jack Black, Paul Rudd, Justin Long and Jason Schwartzman) falls flat, as do most of Dewey's repeated sink-crushing hissy fits—this is one case where the comedy comes at such a brisk and enlivening pace that it hardly matters when a scene fails. Wait another minute, and you'll be laughing again, sometimes to the point of tears.

The screenplay by Jake Kasdan and current "It"-filmmaker Judd Apatow works gangbusters, showing off an accurate knowledge for the predictable narratives of true-life musician-based dramas and then blissfully skewering them in R-rated fashion. The tragedy from Dewey's childhood, which mysteriously causes him to lose his sense of smell, is as savvy as it is over-the-top. When success first comes and Edith feels jilted, Dewey tells her that he cannot build her the candy house she wants because it would melt. "Not if it doesn't rain," Edith replies. Dewey's drug problems in adulthood, not helped by drummer Sam's (Tim Meadows) pleas for him to not try pot, cocaine, LSD, etc. even as he prattles off only their positive characteristics, leads to a hilarious sequence set at rehab. As his withdrawal symptoms take him from feeling cold, then hot, then cold and hot at the same time, the harried nurse yells to the doctor that "he needs more blankets and he needs less blankets!"

In regard to Dewey's love-hate-and-back-to-love romance with Darlene—hints of June Carter Cash, anyone?—they share a sex scene involving bashful feelings, lust, physical violence and strangulation that is as ridiculous and it is priceless. When his drug habits and erratic behavior get to be too much and she leaves him, the viewer is surprised that they actually care about them as a couple, leading to a reconciliation between them in their fifties (we know this because Darlene shows up and substantiates that she is "age fifty") that is affecting and loopy in equal measure. Oh, and one would be remiss not to mention Dewey's 1960s stint as an uncanny Bob Dylan wannabe—cause for perhaps the film's heartiest chuckle—his incomprehensible, nonsensical lyrics utterly perplexing the backstage people as well as the audience.

Character actor John C. Reilly's filmography, up until a year or two ago, was mostly marked with roles allowing him to show off his dramatic chops. With 2006's "Talladega Nights" and even more so here, Reilly proves that he is equally brilliant at comedy. As with any troubled musician type, Dewey Cox is infuriating, making too many mistakes to count, and yet it's easy to see why he is so endearing to fans. Reilly does not merely essay this character with one note, but develops him throughout into a three-dimensional human being; it's all in good fun, but the actor treats it with the same seriousness he does any other part, and the picture is better for it. As first and second wives Edith and Darlene, Kristen Wiig (2007's "The Brothers Solomon") and Jenna Fischer (2007's "Blades of Glory") lend welcome, always game support, as do a huge host of cameo appearances from everyone from Jonah Hill to Jane Lynch to Frankie Muniz to Harold Ramis.

Jam-packed with wall-to-wall original songs that irresistibly compliment Dewey's journey through the twentieth century (any one of them could deservedly be up for an Oscar nomination), "Walk Hard: The Dewey Cox Story" is one of the more enjoyably undemanding releases of the last few months. Whereas most prestigious end-of-the-year efforts are jockeying for awards notices, here is a film with the single-minded goal of making the audience guffaw. Raunchy, broad and yet intelligent, "Walk Hard: The Dewey Cox Story" is a go-for-broke slapstick, but, in its own surprising way, it is sweet and kind of touching, too.