live Verdi Festival: La Traviata; Alzira Royal Opera House, London

It was love at first sight. Just as it will be for their next performance. And their next. Opera's golden newly-weds, Roberto Alagna and Angela Gheorghiu, now have an obligation to their public. Indeed, such has been the media's appetite for pushing at the boundaries between life and art that it came as something of a relief to find Miss Gheorghiu's Violetta in such excellent health. Her well-deserved triumph on Monday night gave further notice of a career which is already delivering more than it promised only a couple of seasons back.

This is a glorious talent, so much so that we should start fretting now about its future welfare. The voice itself has freedom and flexibility and warmth, an engaging creaminess of cover over the entire compass. But add to that her musicality, her natural ability to find the emotional centre of every phrase, to make that magical connection between the letter and spirit of the score, and you've a recipe for enchantment. Would that her "other half" shared it. In Act 1 of La Traviata they share the same music, but it's what they succeed in expressing through that music that illustrates the extent of the artistic distance between them. "Love is the heartbeat of the universe - mysterious, exalted, both pain and pleasure," sings Alfredo, but I don't see "behind the eyes" of Alagna's phrasing. It's too plain, unyielding, resistant to the vocal endearments that are its heart and soul. It's as if we've now heard his entire vocabulary. Gheorghiu, on the other hand, will constantly surprise you with new colours, new shadings, new intensities. When she sings "My body is in pain, but my soul is in peace", that's what you hear. Not the singer, not the technique, everything but. A numbing fragility. In despair that she will die so young ("Gran Dio! morir si giovane") she rallies with a darkening defiance in the voice. For a moment, she believes, you believe, that she will live for ever. Don't miss her.

A second cast (a third in the case of pere Germont) may yet provide other good reasons for revisiting Richard Eyre's dressy but dramatically bland staging (which in one sense - and isn't this the curse of the repertoire house? - makes it so much easier to revive). Unfortunately, you are saddled with the same conductor, Simone Young, throughout the run. Her sole contribution to this evening was a forceful, generalised energy which at best skimmed the surface of Verdi's best intentions, at worst press-ganged cast and orchestra into some decidedly awkward corners.

To hear Mark Elder, "in concert" on the following night, find nuance and fascination and a keen selective energy in a score far less well-endowed than Traviata was to appreciate the extent to which a true Verdian can breathe life into even the still-born. There is an exuberance, a lust for local colour, about Verdi's Alzira, but none of it, of course, has very much to do with Peru. Parma, more like. But the colours - the piping hot wind bands of the streets - despatch their own vitality, and the reedier timbres of the Orchestra of the Age of Enlightenment woodwinds (not least their wonderful first clarinet, Antony Pay) were here deployed to delicious effect. Elder makes no apologies for Verdi's infelicities, kicking up the dust of those beery chorusings with rude abandon. Period trumpets and trombones lend a welcome rasp to the sound (the latter forming a marvellously mysterious alliance with two double-basses in the prelude to the penultimate scene) while gut strings are quite simply all the stringier for it.

Now, if the singing had been on that level... Well, in one sense it was. Unstinting. Rapacious. All thoughts of bel canto banished to the previous night's Traviata. At least Alexandru Agache's Gusmano was a touch of class, a sporadic reminder of the value that might be placed on beautiful sound, not for its own sake, but as a meaningful extension of the vocal line. Is it not depressing that a young singer like Keith Ikaia-Purdy (the tenor hero Zamoro) should as yet show no evidence of being able to sing a grateful, well-sustained legato? The voice has a distinctive baritonal girth to it, and he can whack out the big notes like he means business. But the real business of fine Verdi singing is about style. About artistry. Not attitude. The Chilean soprano Veronica Villarroel (Alzira) was all attitude and precious little artistry. Believing you are a diva does not make you a diva. It was hard, if not impossible, getting beyond the shrill, uneven, unlovely sound, the ill-formed phrasings born of faltering technique. Harder still with Gheorghiu in mind.

n Further performances of 'La Traviata' Sat, Mon, Tues, Thurs, Fri (19) at 7pm, ROH, London WC2. Booking: 0171-304 4000; Mon and Thurs perfs, with Angela Gheorghiu and Roberto Alagna, will be relayed live to the Big Screen in Covent Garden Piazza.

'Alzira' can be heard at 7.30pm, Tues, Radio 3