Just two bits of homework I'd suggest to anyone attempting a ballet of Romeo and Juliet. Read the lines, "How silver-sweet sound lover's tongues by night,/ Like softest music to attending ears!" and "For never was a story of more woe/ Than this of Juliet and her Romeo."

These lovers must speak, sing or dance a poetry beyond ordinary capabilities, and their story must tear us more than any we have ever heard. Being mundane, weedy or gross is not on the menu.

And so to the new version of Romeo and Juliet, produced for the Bolshoi Ballet last year by the Cheek by Jowl theatrical duo Declan Donnellan and Nick Ormerod, and a Moldavian choreographer, Radu Poklitaru, and given its UK premiere at Covent Garden.

To start positively: getting a theatre director into the theatrically outdated ballet world is a good idea. All the ballet versions are imperfect, so no violation is done to a sacred corpse, and Donnellan and Ormerod have produced a strong scenario, economic with characters, well threaded with the music, and with an imposing modern design of slabs of wall and light.

Prokofiev's music is smartly re-edited, often reassigning overfamiliar music to different uses, scenically rather than lyrically. The flow may be disrupted, but the colours of the music, switched on and off like this, act like a sort of aural lighting plan.

Silence is used to stretch out key instants - the opening view of swaying black hostile figures, the moment Romeo and Juliet see each other. The adults are a brusquely sexualised ruling class, whose rutting dances in black cocktailwear offer an obvious provocation to innocent young lovers.

Mercutio and Tybalt are nicely sharpened, with Tybalt impelled to lurch publicly out of the closet on seeing Mercutio done up in drag, to the horror of the hormone-overloaded Lady Capulet. The leading performances are all sparky and magnetic, the urchin Maria Alexandrova and rosy-cheeked Denis Savin as the lovers, Denis Medvedev, Yuri Klevtsov and Ilze Liepa as the supporting trio.

But positives run out just as we reach the central element. The choreography looks as if Poklitaru fast-forwarded videos of the ballroom dances in Matthew Bourne's Swan Lake, and reckoned he could do this. He can't. The adult chorus/crowd is adequately manipulated, but the lovers, far from soaring over them, become quite ridiculous whenever alone together.

Romeo's main motif is to shudder all over, like a dog exiting a pond. If he could speak he'd stutter and gulp, there'd be no "Ethiop pearls" and "empty tigers". Juliet jogs about, giggling and gangly, flinging herself on to Romeo's back with cocked legs; if she could speak, she'd go: "Like, hi."

The death and love duets are virtually interchangeable, with a bony, heavy gawkiness that comes straight from love-making. Most of us probably do this at home, when the back isn't too bad, and if we glimpsed it in the mirror there'd be an embarrassed end to sexual reproduction.

Dazzling passions? Legendary lovers? In Mercutio's words, they have made worms' meat.