First things first: Jonathan Fensom's set for Little Shop of Horrors is, in every sense, terrific. As you walk into the larger of the West Yorkshire Playhouse's two auditoria, it towers massively to dominate everything, a brilliantly detailed evocation of Skid Row all the way up to the metro rail bridge, which is the only real sky to the bums below. A thing of great beauty in its own right, if we're truthful, Fensom's creation is way above and beyond the call of duty, since only a small proportion of it is ever used in this overblown production of an essentially small-scale musical.

Little Shop of Horrors is a spoof of those horror B-movies of the 1950s, itself based on the 1960 film of the same name by Roger Corman. His aim, apparently, was a satire on the more ludicrous sci-fi movies that were creeping onto the scene, but by turning it into a stage musical, Howard Ashman and Alan Menken blur too many edges, and in this production, directed by Christopher Luscombe, it's no longer clear whether our spoof is intended to be pastiche or parody, homage or high-campery.

The plotline doesn't help. Orphan geek Seymour (Jeremy Finch, who could usefully deploy considerably more of the physical ineptitude of the young Jerry Lewis) is protectively employed in the failing florist shop of Mr Mushnik (a fine classic Yiddish patron from Jack Chissick) - as is the girl he worships, insipid Audrey (Josie Walker), who's trapped in a violent sado-masochistic relationship with a biker dentist.

As the business collapses around their ears, Seymour discovers that a strange plant he found on the day of a solar eclipse thrives and grows more than incrementally on a diet of human blood. In B-movie terms, this would be a cue for some great Grand Guignol; or in competent parody, a lever for a barrel of laughs. This Little Shop of Horrors gives us neither.

Perhaps it's just dated. The songs - splendidly belted by the lively street trio of Gabriella Khan, Veronica Hart and Me'sha Bryan and given pure, strong voice by Walker (whilst Finch and Chissick are completely drowned by a crazily over-amplified five-piece band) - vaguely recall Grease but are in themselves utterably unmemorable. And the lyrics - especially in a number like 'Mushnik and Son' which cries out for Jewish humour - remain as stubbornly witless as the rest of the book. There are just three good laughs in the show: the tortured rhyming of "greatest" with "semi-sadist", the reprise by Audrey of her longing for 'Somewhere that's green' just before she collapses into the mammoth maw of the ravenous vegetable, and, er, I can't recall the third.

It is impossible to fault the work rate of anyone on stage, but sadly they work their butts off in a show that has an aching void at its core. The WYP audience, which is never slow to cheer theatrical magnificence, applauded the energy of the performance but remained more muted than the actors at the curtain.

- Ian Watson