A Midsummer Night's Dream, Royal Opera House, Linbury Theatre London

Right at the start of Britten's Dream, a series of rising and falling string glissandos, highlighted by piercing shimmers of light at their peaks, leads us from the everyday world into the enchanted Athenian wood. The freewheeling harmony swings back and forth, up and down, disorienting the listener and taking its time to settle. The music tells us straightaway that we're in strange and potentially dangerous territory, where almost anything could happen.

As with the rest of the score that follows, this memorable opening is caught in this Royal Opera production with deft sensitivity by the Linbury's visiting pit orchestra, the City of London Sinfonia, under the perceptive baton of Richard Hickox. Musically, this is one of those pieces that show Britten's feeling for instrumental colouring at its most refined and telling. Few 20th-century operas conjure up such a ravishing and varied sequence of images in sound.

So what does Olivia Fuchs's production come up with to match this extraordinary opening? The members of the cast playing Theseus, Hippolyta and the four lovers enter in modern dress, sit down in theatre seats and fall asleep. Is this meant to be a cheap joke at the audience's expense? And whatever happened to magic? That, really, is the element in shortest supply throughout the evening - at least from a visual perspective. The Linbury's infinitely adaptable auditorium proves well-scaled for the piece. Niki Turner's designs include fragments of Shakespearean text set high on the walls like a frieze, though what we are presented with on the stage itself evokes nothing so much as a display of shelving at your local Ikea, only with fluorescent lighting round the edges. Jon Driscoll's video projections at least manage to supply the apt image of an ominous owl. But more than is usually the case with this opera, what we're looking at is nowhere near the quality of what we hear.

Some of which is very good. The boy fairies (courtesy of the Tiffin Boys' Choir) are musically thoroughly prepared, though they often look at a loss dramatically. This pyjama-clad troupe, more JM Barrie's Lost Boys than elfin elementals, also lacks the sense of weirdness and menace they need to balance the show. Visually, neither William Towers's Oberon nor Gillian Keith's Tytania quite registers with an essential other-worldliness either, but he in particular offers an ethereal, unearthly tone that sends an authentic shiver down the spine, while her coloratura flights of fancy are precise and sparkly.

The lovers too are a pleasing group vocally, though their scenes are under-directed. Their music offers far more tension, far more highly charged emotion than either the insubstantial glitter and eerie sweetness of the fairies, or the galumphing vigour and rough-edged four-squareness of the mechanicals. But the twists and turns of their amorous engagements and disengagements need the clearest exposition, and here only Grant Doyle's Demetrius makes a consistently full-on impression, though Robert Murray's Lysander, Tove Dahlberg's Hermia and Katie Van Kooten's Helena all have their lyrical moments.

As so often with Midsummer Night's Dream, it's the mechanicals that provide the most fun in the show, given that their scenes are virtually fool-proof and that Britten writes some memorably witty and devastatingly spot-on send-ups of Italian opera for their Pyramus and Thisbe parody. (Apparently Joan Sutherland's recent triumph in Donizetti's Lucia di Lammermoor at Covent Garden was one of his targets when he composed the piece in 1959-60.) Andrew Kennedy enters fully into the vaudeville aspect of these scenes with his amiably daffy Flute, and he looks a peach in a pink dress as Thisbe. Jeremy White's Snug is impeccably crafted and Darren Jeffery's Bottom manages to remain likeable even at his most bumptious and impossible. Andrew Sritheran shows promise as a gangly hunk of a Snout, but as organiser of the workers' co-operative of players the normally reliable Jonathan Best makes a curiously muted Peter Quince.

In the final scene on troop Mark Beesley's forthright Theseus and Liora Grodnikaite's elegant Hippolyta for a return to something approaching normality, though of course the fairies have the last song and Jami Reid-Quarrell's super-athletic Puck - the most brilliant physical performance in the show, incidentally - is allowed the last word. Though it ends well it's been a patchy enterprise, leaving the stubbornly abiding impression of a less than enchanted evening.