Welsh National Opera has given Monteverdi's `Coronation of Poppea' a sonic and visual make-over. But, asks Stephen Walsh, is it still the opera the composer intended?

Monteverdi's final drama about sex and power in Nero's Rome has got longer and thinner since the Leppard era in the early Sixties, when it played for a couple of hours sheathed reassuringly in swooning strings. The new Welsh National Opera staging, which opened on Thursday (a co-production, though, with the Bavarian State Opera in Munich, which saw it in July), lasts almost twice as long and with less than half the clothing.

Why play this rambling, antiquated, unfocused masterpiece at all, asks one of the programme articles rhetorically. The Cardiff audience, who enjoyed David Alden's high-camp production as they will no doubt enjoy Aladdin here in a fortnight's time, may well have felt that, without some such whooping-up, this lovely but remorselessly short-winded music would indeed be hard to endure. But that be cold comfort for the admirable Rinaldo Alessandrini, whose edition is being played, and who directs the performance.

Alessandrini is a baroque specialist who takes pains over musical detail. With him, one doesn't just get educated instrumental playing, but educated singing, with colourings and ornaments that really do carry an expressive cargo, instead of the relentlessly "learnt" trilli of early early music. Certainly the techniques are not without their problems. Beside much beguilingly sensuous work from, especially, Catrin Wyn Davies as the future empress Poppea and Sally Burgess as the outgoing empress Ottavia, there was, on Thursday, a lot of out-of-tune singing, some rough tone, and - in a few cases - an uncertainty about how to give these long ariosos expressive interest without corrupting the line. Much of this may settle down before the staging returns for next year's tour (oddly, it was only receiving two performances in Cardiff this season) and we'll be left with at least a musically coherent view of what is probably, after all, the work of more than one composer.

The production, meanwhile, is on a different planet. Alden takes his cue from the picaresque episodes, which do invite camp treatment, and get it, brilliantly, for instance from Neil Jenkins as the multiply-bewigged and handbagged maid Arnalta, and from Linda Ormiston as Ottavia's Nurse, alias an over-the-hill, over-the-top Red Cross attendant.

But when these idioms leak far into the tragic channels of the plot, the water gets muddy and the going tough. When Seneca (a bore, perhaps, but the moral focus of the drama) is tracked by three little note-taking red-quoiffed Tintins; or gets his cards from a mummified Mercury, Alden's agenda decisively abandons Monteverdi's. From a morally aware but cynical study of human conduct, the drama turns into a pageant on the vulgarity of power - which is fair enough, but another work; until, that is, the one genuinely beautiful, coherent moment of the evening, when Ottavia bids farewell to Rome amid a psychedelic nightmare of black-and-white tiles, for which unforgettable tableau I can forgive designers Paul Steinberg and Buki Shiff the office fancy-dress party that is the rest of the production.

Still, in its own terms, the evening has its strengths. Paul Nilon, a tenor rather than soprano Nero, hits off the character's febrile, womb- clutching inadequacy - pretty in neither sight nor sound - while Ms Davies gratifies him, at first, with irresistible sensuality, turning gradually to the vulgarity that is the true (in her case visible) under-belly of power. Gwynne Howell, as a chain-smoking, Guardian-reading Seneca, belongs vocally in a different production but is welcome in this one. Linda Kitchen is a nice Miss Moneypenny of a Drusilla; Michael Chance a fluent, if one- paced, Ottone; Linda Tuvas a suitably boyish Amor, perched, however, for some reason, on revolving doors that flash a disagreeable light onto the paying customers, if not onto the work.

On tour February-April 1998. Information from 01222 464666