La Finta Giardiniera, Royal Opera House, London <!-- none onestar twostar threestar fourstar fivestar -->

The boy Mozart had promise

Not everything in the garden has been rosy for La Finta Giardiniera. Losing the director Christof Loy over disagreements about cuts with Sir John Eliot Gardiner was not a good start. That's like fighting over the weeding before beginning the planting. It would be interesting to know where the disagreements lay, because this overlong product of Mozart's 19th year probably needs more ruthless editing than was in evidence here.

The fascination lies in seeing his dramatic genius in embryo, in watching him learn on the job. La Finta Giardiniera is full of pointers to the future: we recognise the characters and situations, but not yet who they really are and why they are there. The landscaping leaves a lot to be desired.

Enter the garden of intrigue: it might even be the last act of Figaro (witness the climactic nocturnal scene of mistaken identities). A wedding is in the offing and a battle royal of class and sexual prejudice is up and running. But as one character puts it: "I'm not quite sure what is happening but things are not quite what they seem." Too right.

Mozart's long exposition lacks direction. It's a succession of frozen moments, arias without context. They momentarily dazzle and delight, but to use an appropriately sexual metaphor, they are all foreplay and no consummation. Not until much, much later in the evening. How do you make that work in the theatre? With difficulty.

Perhaps Christof Loy was well out of it. His assistant Annika Haller does what she can based on what Loy did in a previous staging from 1998, but characters are so underdeveloped and plotting so wayward that a well-dressed concert performance is the best one can really hope for. Herbert Murauer's elegant garden terrace hardly helps in practical terms. A downstage water feature pushes most of the action upstage and too much mileage is spent having characters teeter on its edges or recklessly (and pointlessly) getting wet.

But enough of what isn't there. Here's what is: the English Baroque Soloists cajoling, fizzing with energy from their elevated pit. A bright, verdant sound, shapely and dynamic under Gardiner's elegant and brilliant direction. And seven engaging performers. The seasoned Mozartian tenor Kurt Streit showed his authority as the Mayor, Don Anchise, landing the first of Mozart's musical jokes with an aria expressing his feelings entirely in musical terms. Gardiner's underscoring rose to the conceit.

Sophie Koch's lovelorn and dusky-voiced Ramiro (Cherubino in waiting) was happier in legato than coloratura, though the memory of a sticky opening aria quickly faded. The suave Christopher Maltman's Roberto (Nardo) was afforded the best foreplay of all, coming on to Patrizia Biccire's feisty maid Serpetta (Despina in waiting) in three different languages - including (good joke, this) heavily accented English.

Don Anchise's niece, the bride-to-be Arminda, is a Milanese clotheshorse with a waspish waist and a tongue to match, and Camilla Tilling was with every spitting consonant the cat from the catwalk. One of Mozart and his librettist's best ideas here was to make a virtue of the mismatch with Robert Murray's energetic Count Belfiore and turn their foreplay into one long spat, the joke being that the chastisement is slowly but surely growing on the Count.

Finally, a voice, a singer to watch. Genia Kühmeier as Sandrina (the counterfeit gardener of the title) is the possessor of the truest, bell-like soprano. The honesty of her singing, and the total absence of affectation, make her an exciting prospect. It was a pity that the voice refused to scale down to Gardiner's ear-pricking level of quiet rapture in her first aria, but in her big hallucinatory scena in Act Two ("Crudeli, fermate, crudeli") she seized the startling, palpitating originality of it with everything she had.

In an instant, Mozart's future was scarily immediate.

Until 7 October (020-7304 4000)