This is a festive season, a time to gather with friends, a time for merriment.

All of which comes to explain how I had two martinis before I sat down to watch "Walk Hard: The Dewey Cox Story."

Or was it three martinis with two olives apiece? I don't remember. I do remember laughing heartily throughout "Walk Hard," a parody of musician bio-pics featuring John C. Reilly as a roots-rocker who, like his music, just won't die.

A second caveat: "Walk Hard" is the kind of movie that's going to sit particularly well with critics, who've had to sit through a lot of biopickin' these past few years - there've been at least four, or 10, if you count all of the Bob Dylans in "I'm Not There." (You think we've forgotten about "Beyond the Sea"?)

Most seem to begin with some horrible rural accident that causes its protagonist to go blind or wear black, a theme duly noted by "Walk Hard," which begins with young Dewey severing his more-talented, more-loved brother in a machete fight.

The haunted Dewey (a consistently dense Reilly) channels his guilt into his music, which, over the next several decades, phases through rockabilly, country, punk, psychedelia, balladeering, high Beach Boys, hip-hop.

He also channels his guilt into unchecked consumption of illegal drugs, each introduced by his hard-partying sideman (Tim Meadows) who dutifully lectures Cox on the evils of every drug he supplies to him.

Much of "Walk Hard" is eagerly lowbrow - one running gag makes a farce of Hollywood's fear of full frontal male nudity. But some of the comedy is quietly smart, especially the music, all assembled by top musical talent.

The highlight is Dan Bern's hilariously abstruse approximation of a Dylan song - a parody lacerating enough to indicate why Bern was once banned from the Philadelphia Folk Festival.

Like all biopic musicians, Dewey prefers rehab to family, but finally comes around to recognize his paternal obligations. In one hilarious scene, he throws a football on the beach with all 27 of his illegitimate children.

"Walk Hard" ends with the sort of mawkish tribute/retrospective that famous musicians probably overdose in order to avoid - an event hosted by a famous alt-rock moper and mumbler, who proves that he has a sense of humor after all.

Stay tuned through the closing credits, when Cox's music becomes truly immortal, and we finally get a look at the "real" Dewey.

Produced by Judd Apatow, Jake Kasdan, Clayton Townsend; directed by Jake Kasdan; written by Judd Apatow, Jake Kasdan; music by Michael Andrews; distributed by Columbia Pictures.