Bird Of Night, Royal Opera House, London <!-- none onestar twostar threestar fourstar fivestar -->

When the Trinidad-born Dominique Le Gendre unveiled a 20-minute chamber piece as part of Covent Garden's theatre festival A Nitro at the Opera in 2003, one of eight black artists commissioned to contribute, it was clear that something larger was struggling to get out.

Here that something is, illuminating in every sense of the word the Linbury Theatre's subterranean black box. A brightly lit walkway curves round the stage and vanishes up into the darkness: a simple device, but a very effective way of introducing fantasy and mystery into this stark, rectilinear world.

The orchestra strikes up a merry, vibrant sound, and a girl in a white shift lies down to sleep; two men materialise beside her like bleached apparitions, and burst into song. A line of children appears, then a line of pipe-smoking women with parasols, followed by a line of discreetly acrobatic dancers: all look Caribbean, with the men in straw hats and the women in floral dresses, as befits this opera's time and place.

This is Trinidad in the Fifties, a land just emerging from its colonial wrappings. The story has to do with a teenage girl who's emerging too, but her path is not yet clear. While Appolline's family want her become an educated lady in France, she's more interested in becoming a "bird of night" like her godmother Nen-Nen: she wants to escape into the realm of her island's magical folklore.

And that folklore is soon all around her: first glimpsed as a bright red wing waving out from behind a pillar, then with a line of angels, then with a flamboyantly stylish couple kitted out as though for Come Dancing - these last being Diego and Désirée, alias the Devil and his wife. And yes, the story is as just complicated as you'd expect, given the elaborated nature of Trinidad's sacred-secular ties.

It's appropriate that the director, Irina Brown, and the designer, Rae Smith, should have staged it with the pizzazz of a West End musical, using constant coups de théâtre: their bird-men make a gloriously fantastical chorus-line.

If the music intermittently echoes Britten's A Midsummer Night's Dream, the staging evokes Judy Garland and the Yellow Brick Road, and in Betsabee Haas they have a suitably wide-eyed and impulsive performer in the main role. Her top notes may disappear, but she sings with such sweet characterfulness that criticism is disarmed.

Le Gendre is a skilled orchestrator with a knack for combining strings, harp, and marimba, and has a sensitive feel for the human voice; she can bring the auditorium to stilled rapture with a pastiche Negro spiritual, or galvanise it with a genuine Cuban groove.

Meanwhile, Le Gendre's librettist, Paul Bentley, deftly mingles Creole locutions with brightly coloured literary extravaganzas. So why does this production, despite its megawatt charm, and despite the heroic performances of its orchestra and cast - notably Paul Whelan and Andrea Baker, as the heroine's father and godmother - disappoint?

For a start, the dramatic effects - from Appolline's winsomeness, to those endlessly paraded big red wings - are laid on too thickly, and one gets very tired of them by the end.

Second, the pacing is wrong: emotions are almost constantly at fever-pitch. Third, the densely freighted libretto is largely inaudible: my eyes were constantly flicking up to where the surtitles should have been in an instinctive attempt to understand what was going on, and when speech replaced song for a couple of minutes, it was as though a fog had briefly lifted.

Giving us a fortissimo sextet in which each singer has their own agenda is, in these circumstances, an absurdly over-ambitious ploy. Any new opera must pass a daunting battery of tests, and it's no shame that Bird of Night should fail some of them.

But nonetheless it has some things resplendently right: Le Gendre and Bentley should take the opera back to the drawing board, slim it down, sharpen it up - and then the sky could be the limit.

To 28 October (020-7304 4000)