A Mighty Wind is a joke stretched too far and too thin, from the team behind essential 'rockumentary' This Is Spinal Tap and much-praised Best In Show. An improvisational comedy which carries the germ of a good idea, it hinges on a memorial concert held for an inspirational record executive, from the acts whose names he made. Broad targets are duly hit in a gentle spoof of the folk scene from co-writer/director Christopher Guest. Simply, it isn't funny enough.

The genius behind Spinal Tap was how it took music cliches and bumped up them up "one louder" - capturing the truth of heavy rock but heightening it for humour. Thus there were songs - about big bottomed gals ("My baby fits me like a flesh tuxedo...") and sex farms ("Scratching in your henhouse/Sniffing at your feedbag..."), which felt both real and preposterous.

But the folk scene is almost self-satirising, with its beardy-weirdy artists and twee trimmings. It takes no great comic gift to recognise its oddities, and the songs crafted by Guest and co are, if anything, too good to be funny. This affords a rare moment of poignancy as long-split 60s singers Mitch and Mickey (Eugene Levy and Catherine O'Hara) recapture their youth warbling A Kiss At The End Of The Rainbow, but it means laughs are in short supply.

"RENT SPINAL TAP INSTEAD"

Harry Shearer is brilliantly deadpan as the boom-voiced bassist of The Folksmen, while Fred Willard (the commentator in Best In Show) excels as a small-time manager living off the catchphrases of his failed TV show.

Don Lake gives an honest turn as the son who couldn't stand his father's folk obsession, and Jane Lynch impresses as newly-found folkster Mrs Bohner. But her name is a limp gag about a porn star past, suggesting the level of invention on offer. This is cheap, and worse: not funny. Rent Spinal Tap instead. A Mighty Wind won't blow you away.