Tenors really don't last very long these days. With the vocal glory of Rolando Villazón fading fast, his Peruvian colleague Juan Diego Flórez drew a capacity audience of tenor-hungry punters to the Barbican for a programme of music by Rossini, Bellini and Donizetti. With plenty of overture fillers from the dutiful Orchestra of Welsh National Opera, conducted by Carlo Rizzi, there were a mere 33 minutes of bel canto blockbusters on offer - but Flórez scarcely made it to the end.

Just before he was to launch on yet another paean of lovesick praise to yet another angel of a woman (Ange si pur, from Donizetti's La Favorite), there was a long silence. A Barbican official strode on to the stage, summoning the conductor off into the wings. Had Flórez done a runner? It turned out that he wanted a little talk with Rizzi - and a quick hot shower - to attempt to banish an onset of phlegm. Flórez returned at last, giving us a witty disquisition on that bodily fluid - and sang Pitie, Seigneur! with rather more emotional conviction than before.

On, finally, to the nine top Cs from La fille du régiment. Flórez has been warned against overdoing this one; but he fired off the high notes one by one, mopped his brow, placed his hands on his heart, and obliged with a single encore of the Barber of Seville's gurgly cabaletta - sinuses, larynx and lungs enjoying one final moment of triumph.

And the rest of the evening? Well, no one would have guessed there was a problem. Except for the eternal one which faces those who are not paid-up members of the fan club. Whether sculpting a long sigh of song in the laments of Bellini's I Puritani; whether probing the dark Gallic abyss of exile in Rossini's Guillaume Tell; whether throbbing with passion as the rejected lover of Donizetti's Lucrezia Borgia - in all this, Flórez uses one single gear, one expressive mode, one universally applied vocal colour. And to make this music live - rather than use it merely as a vocal workout - there must be so much more.

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