Writer-director Christopher Guest -- king of the mockumentary genre -- returns to his musical oddball roots in "A Mighty Wind," a "This Is Spinal Tap" for the 1960s folk-pop crowd.

As amusingly deadpan as 2000's dog-show-spoofing "Best In Show" and 1997's community-theater send-up "Waiting for Guffman" -- and featuring many of the same actors -- Guest's new film is similarly quirky, ironic and inexplicably endearing as it follows the preparations for a big concert featuring the reunions of several aging, corny, melodiously mellow fictional folk bands that were never as harmonious off stage as they were on.

It's a picture packed with wonderfully pokerfaced performances from the likes of Michael McKean, Harry Shearer, Eugene Levy, Catherine O'Hara, Bob Balaban, Fred Willard, Parker Posey and Guest himself -- most of whom play washed-up but unnervingly (sometimes unnaturally) chipper singer-songwriters. It features a steady stream of Guest's hilarious non-sequiturs (references to Shetland pony polo leagues and a low-budget record label that saved money by not putting holes in the center of its LPs) that are sure to please fans of his other flippant flicks.

It has the same kind of improvised interview sequences in which the talented cast develops its where-are-they-now characters through the manifestation of funny foibles, eccentricities and back stories ("There had been abuse in my family," pines Levy, "but it was mostly musical in nature"). And up to a point it's just as entertaining as its predecessors.

But the more Christopher Guest films one sees, the more they start to feel the same -- and in "A Mighty Wind," the writer-director drops most of the satirical spirit to spend the last reel or two actually presenting the climactic folk concert in its too-straightforward entirety. It seems as though he might have gotten so attached to the characters that he sincerely wanted to see them belt out their tongue-in-cheek hits.

Had the awkwardness and rivalries stirred up by the reunion hijacked the proceedings, "A Mighty Wind" could have keep the snickers coming and might have been a mighty good comedy. Instead it's a passably amusing art-house lark -- perhaps worth the price of a matinee, but certainly nothing to sing about.