TO BE credible in the title role of Handel's Giulio Cesare it helps not to be dressed as something out of The Avengers c 1968. Every time Ann Murray comes on in the new Royal Opera production, looking like a diminutive Diana Rigg, it doesn't do much for the operatic sleight of hand that casts a woman (you're not supposed to notice) as the conquering hero of the ancient world.

But then, Handelian opera is a carnival not just of gender-bending but of travelling through time. And Lindsay Posner, the director here, has followed the trend in Handel stagings with a show that re-enacts the carnival in terms of stylishly postmodern whimsy. Bite-sized jokes, a spot of camp.

The problem is, he doesn't play the game as cleverly or with the sharpness of a Nicholas Hytner or a Peter Sellars, and it settles into bland restraint with set designs that probably looked Conran Shop on paper but have ended up John Lewis in practice. It's all too damned modest.

But that, I suppose, is in keeping with the new, toned-down culture of the Royal Opera. For Giulio Cesare is the first RO (alas, no longer ROH) presentation at the Barbican Theatre, which feels spartan, soulless and Blairite after the familiar plush and buzz of Covent Garden. There's a new champagne kiosk in the foyer. But it stands forlornly under-patronised: the concrete spaces of the Barbican don't seem to suit champagne. And as for the auditorium, the pounds 1.9 million which has been spent on adapting it to the needs of opera has resulted in something with better sightlines and contact with the stage than we ever knew in Bow St, but a restricted performance space (no room for chorus spectacle) and a boxed-in sound that isn't positively bad but doesn't bring the colour or immediacy of the voices into focus.

The casting for Cesare is another sign of the times: its British-American bias is more upmarket ENO than conventional ROH. Ann Murray's singing sacrifices too much tone to a sort of barking Sprechstimme on the lower notes of recitatives; but it is wonderfully expressive, delivering text with an intelligence and clarity that few other stars of this repertory can match.

There's also some superbly well-defined countertenor singing from Brian Asawa, who plays Ptolemy as a retarded Rastafarian, and from David Daniels as a big-baby Sextus - although I'm not convinced that a countertenor is the best voice to use there. Sextus was never a castrato role. Handel wrote it, initially, for a woman in drag, and the inter-voicing of the duet with Cornelia at the end of Act I demands (to my ear) that it remains a female sound, however striking the countertenor alternative.

Ultimately, though, this opera stands or falls by its Cleopatra, perhaps the most covetable role in all Handel. And the Royal Opera's Amanda Roocroft is certainly impressive: strong, secure, with an extensive range and well- articulated coloratura that meet the broad demands of her eight arias. But it's a hard sound, and it doesn't yield much to the tenderness of her laments or to the ravishing "V'adoro pupille" which ought to be the ne plus ultra of aural seduction. Ivor Bolton conducts.

It's been an eventful week at the Coliseum. On Monday English National Opera welcomed a new music director, Paul Daniel. On Friday it announced the sudden departure of its managing director Dennis Marks. Daniel made his first appearance in a new Flying Dutchman and - resisting wisecracks about ENO being a famously unhappy ship - I can only say it had promised to be something special. In fact, the first 30 seconds were literally electrifying, as lightning cracked across the stage and the opening chords punched hard and lean, like clenched fists, from the pit. But then the tempi settled into slowness, and the attack wore thin. So did what had initially seemed the boldness of the staging.

Devised by a Norwegian production team under director Stein Winge, it is all sculptural abstraction. No ghostly boats. Just skeins of air-pumped parachute silk heaving like the sea, and a enormous cantilevered frame woven across with rubber strips. Because the under-side is red you know it represents the Dutchman's sails; and when the Dutchman makes his first appearance, wriggling through the rubber weave, you know it signifies the barrier between two worlds. But then everyone else on stage wriggles through it and the symbolism gets lost - along with any sense of conviction in the cast. Rita Cullis's Senta is forcefully done, a heroic struggle with high-lying notes, but without the voice or personality to fit the role. Willard White's Dutchman is disappointingly unspiritual - unless muscle in a T-shirt is your idea of transcendence - and never as sonorous as one expects that voice to be. The best singing comes from David Rendall's Erik, and the pity is that the production makes so little of him.

But then, nothing could ask less of a character on stage than Welsh National's new, nihilistic Fidelio, just opened in Cardiff. A complete bore, wretchedly miscast and musically misjudged, it's a production where you spend two- and-a-half hours watching blank performances on a bare stage, waiting for something to happen. And in the hands of Patrice Caurier and Moshe Leiser, the joint directors, it doesn't.

Of the singers, Suzanne Murphy's Leonore is thin-toned, Donald McIntyre's Rocco no more than the echo of a once-distinguished voice, and Adrian Thompson's Florestan has (as always) the trumpet presence of a big, potentially beautiful sound betrayed by too broad a vibrato. Only Gidon Saks's strong Pizarro and Rebecca Evans's touching Marzelline gave the evening any lift. And if the brutality of Carlo Rizzi's conducting was representative of his approach to Beethoven, I'll pass on his next symphony cycle. So brittlely regimented was the final scene, it sounded like rejoicing through wired teeth.

The rejoicing of the Last Night of the Proms was only slightly tempered by the dying embers of national grief - in deference to which the BBC ditched John Adams' exhilarating but tactlessly titled Short Ride in a Fast Machine in favour of "I Vow to Thee, My Country". Fortunately, there were no problems with the evening's new work, which was tact itself: a Sanctus setting written by Judith Weir as her contribution to a Requiem commissioned from various composers several years ago in commemoration of the Second World War. The whole thing exists on disc, and it's an odd rag-bag of styles. But Weir's Sanctus is all French restraint - almost an homage a Durufle - and so self-effacing that the score is open-ended, designed to slip into the flow of what precedes it and comes after. Extracting it from the original context, the BBC decided to supply something else for this Sanctus to slip into and scheduled a Messiaen organ piece that was culturally appropriate but confusing for the audience - who cheered the organist Wayne Marshall and forgot about Weir. The tactful Beeb ought to have seen that coming.

`Giulio Cesare': Barbican, EC2 (0171 304 4000), Tues & Thurs. `Dutchman': ENO, WC2 (0171 632 8300), Wed & Fri. 'Fidelio': Cardiff WNO (01222 878889), Sat.