La Rondine, Royal Opera House, London

It is La traviata meets Die Fledermaus. Traviata without the fatality; Fledermaus without the frivolity. Puccini's La rondine (The Swallow) can never quite bring itself to be operetta (despite the Viennese source of its commission) but nor can it quite surrender to tragedy. There's a sense in which audiences have never quite known where they were with it. Until, that is, EMI cemented the real-life romance of opera's golden couple - Roberto Alagna and Angela Gheorghiu - and walked off with just about every award the recording industry had to offer. That was in 1998, and neither the opera, nor the singers, nor the conductor Antonio Pappano have ever looked back. This 2002 staging was the fruit of their collective success.

It is La traviata meets Die Fledermaus. Traviata without the fatality; Fledermaus without the frivolity. Puccini's La rondine (The Swallow) can never quite bring itself to be operetta (despite the Viennese source of its commission) but nor can it quite surrender to tragedy. There's a sense in which audiences have never quite known where they were with it. Until, that is, EMI cemented the real-life romance of opera's golden couple - Roberto Alagna and Angela Gheorghiu - and walked off with just about every award the recording industry had to offer. That was in 1998, and neither the opera, nor the singers, nor the conductor Antonio Pappano have ever looked back. This 2002 staging was the fruit of their collective success.

Anyway, here it is again - not the hotly awaited reunion but a welcome revival built around the "reckless rapture" of its soprano star. And here she is again, in scene one, lending once more her prophetic finishing touches to the poet Prunier's sad song, "Doretta's Dream" - the opera's big hit number. And notwithstanding a tentative moment or two of uncharacteristically flat intonation (occasioned, one likes to think, by the absence of her husband), her lovely voice soars and swoons to the echo. "I fall at your feet," says Prunier (a suitably effete Kurt Streit), but most of the audience are already there.

The sound is still something of a miracle, maintaining its sheath of luxury throughout the compass and even under pressure. And now that Gheorghiu is freer with the portamento that melts and teases and shapes, there is no more beguiling sound on the planet. I still long for her to thoroughly transform herself, lose herself, in a role. At the close of Act I, when she supposedly "dresses down" for a night on the town, the immortal line, "Who would recognise me now?", is suddenly a rhetorical question heavy with irony. And it begs - no, demands - the rejoinder, "And you look fabulous, Miss Gheorghiu".

The production (directed by Nicolas Joël) tries a little too hard to look fabulous. Ezio Frigerio's Klimt-obsessed sets are awash with mosaic, gold-leaf, and - in the Riviera hotel of the final act - a riot of turquoise and emerald stained glass. The applause that greets it says a lot about the audience's dubious taste, though it has to be said that its wow factor is certainly in keeping with the dazzle and glitter of Puccini's score.

There is even a glitter ball in the opera's second act, and it is here that Puccini pulls out his flashiest number: a toast to love as intoxicating as anything in his output, and turned on a key-change that is practically indecent. Emmanuel Villaume, the conductor, embraced and indulged that to sumptuous effect.

But the real substance of the opera is in the heartfelt third and final act, and it was here that the absence of Gheorghiu's "other half", might well have prompted a fresher response from her. For the young German tenor, Jonas Kaufmann, it was quite a debut. The voice is more swarthy and darker grained than that of the Italianate Alagna, and so are the boyish looks. But Kaufmann is a graceful singer weaned on graceful Mozart, and while he can muster a ringing flamboyance for the "money notes", it is the subtlety of his response that draws us in. When he sings of the baby that he hopes that he and Magda might have together one day, the tenderness of his finely attenuated pianissimo singing beautifully reflects the image of the child reaching for the elusive sunlight.

Of course, the child can never be because Magda can never undo her past as a kept woman (shock, horror). But she does get her maid (a feisty Annamaria Dell'Oste) and her benefactor (Robert Lloyd) back. And she does see out the opera centre-stage in a single spotlight. What more could any self-respecting diva desire?

To 26 November (020-7304 4000)