OPERA seasons run like academic years, autumn to summer, and it was back to school this week with a vengeance as Welsh National Opera's new Nabucco, ENO's new Carmen and Covent Garden's revived Le Nozze di Figaro opened on successive nights. Of the three, Welsh National went for the biggest impact, to launch what will be the company's 50th anniversary season and a critical moment in its history, as it awaits the decision on funding for the new Cardiff Bay Opera House. Given the public response to the last, grotesquely mismanaged operatic windfall - Covent Garden's pounds 55m - I can't see the Lottery board rushing into a decision on that one. But they may just take the view that Wales is politically a special case.

The first night of Nabucco was graced by a brigade of MPs bussed in specially for the occasion; and no doubt the significance of what they were watching wasn't lost on them, because Nabucco is an opera about the assertion of national identity and resistance to the yoke of foreign rule. That it proved a turning point in Verdi's career was partly for musical reasons: the characterisation and chorus- writing represents a material advance on the composer's previous work. But the life-changing success of Nabucco's premiere in 1842 was largely due to the political appeal that its quasi- Biblical story of Hebrew slaves and Babylonian oppressors offered to Milanese Italians living under Austrian rule. The great Hebrew lament "Va, pensiero" was tailor-made to become the anthem of the Risorgimento; and whether or not Verdi intended it as such, he was happy to accept the consequent fame and fortune. Sixty years later, "Va, pensiero" was sung, apparently spontaneously, by the 300,000 mourners at his funeral.

But there was another, more potent reason why WNO should open its anniversary season with this piece. Nostalgia. It was a legendary Nabucco that put the company on the map back in the 1950s; and maybe it was the fond, if distant, memories of that old production which caused some of the audience on Tuesday to boo Tim Albery's new staging. Needless to say, Albery doesn't take an Every Child's Old Testament Picture Book line on the piece but provides something starker and harder (claustrophobically boxed-in by Antony MacDonald's sets) that relates the plight of the ancient Israelites to Jewish experience in the 20th century. And before you assume it's just another off-the-peg Holocaust trip, let me add that he doesn't choke the stage with swastikas and Hitler Youth. The point is made more elegantly, in semi-abstract terms; and if anything, his reticence is one of the problems of the staging. It's clear enough that the Jews are Jews, but not clear what the Babylonians are. New Age travellers with machine guns is as far as I got, and jolly silly they looked.

But no matter. They only slightly qualify the fact that, in general terms, this production looks wonderful: handsomely lit and marshalled into strong stage tableaux that make a viable contemporary alternative to the Cecil B de Mille expansiveness of traditional approaches. As for the music, you might take exception to some of the solo singing. Willard White is disappointingly uncharismatic as the Israelite leader Zaccaria, and Janice Cairns's Abigaille rasps like a vocal re-enactment of The Texas Chainsaw Massacre. But beauty isn't everything in singing; and though there are roles I wouldn't want to hear Cairns within a mile of, she is right for Abigaille (a demented warrior-princess) and gives one hell of a performance. There is also, as Ismaele, a hugely promising young tenor: Gwyn Hughes Jones, from whom I've no doubt we'll be hearing more.

But the true stars of the evening are the WNO chorus, orchestra and conductor Carlo Rizzi. Nabucco is above all an ensemble piece, rising to great collective statements, and Rizzi handles them magnificently, as only someone steeped in the idiom of early Verdi could. His tempi are hard-driven, breathlessly exciting, but controlled. He builds a spectacle in sound; and the result, in two words, is world class.

A quality that's in short supply these days at ENO, whose past season wasn't much to shout about and whose new season is playing depressingly safe with what the management calls a "renewal of core repertory". It started on Wednesday with Carmen, directed by Jonathan Miller; and in fairness I should say that it's an enjoyable production, clearly destined to succeed Miller's Rigoletto in the long-term affections of ENO audiences. With a comparably photo-real intensity of detail, it brings the story into the 20th century (the brink of the Spanish Civil War), strips away the usual touristic gloss (not a flamenco skirt in sight), and adds a layer of grime (plus a good deal of stage smoke) to give each scene the grainy, documentary depth of a Cartier-Bresson.

The look of it is endlessly fascinating, the chorus-movement exemplary; and the minor char- acters acquire uncommon prominence, not least because there are fine voices among them such as Mary Plazas (Frasquita), Ashley Holland (Morales) and Katarina Karneus (the 1995 Cardiff Singer of the World, making her house debut as Mercedes). There's also a gorgeous, creamy (if de- consonanted) Micaela from Janice Watson.

But the trouble with this Carmen is that it's rather too successful in demythologising its central characters - to the point where they aren't exciting. Miller has said in interviews that he isn't interested in Carmen as a sexual celebrity - so she becomes a sweatily pugnacious factory worker, elbowing some space for herself in a small world and leaving a trail of pathetic men in her wake. As such, the odds are against Louise Winter ever establishing the charismatic presence that the title role demands; and although she sings well, the voice isn't alluring enough to do the job alone. Robert Hayward's Escamillo has the same problem. And Robert Brubaker's wirily well-projected Jose is such a wimpish mother's boy that he creates a vacuum of negative energy on stage, alienating any prospect of audience sympathy. Add the fact that Keith and Emma Warner's zappy new translation works well for the singing but sounds like lawd- luv-a-duck Ealing comedy in the spoken dialogue, and that Sian Edwards conducts without distinction, and you end up with an equivocal evening.

The Royal Opera's Figaro is Johannes Schaaf's 1987 production revived by other hands and not too impressively, with more comedy but less focus than in the past. On paper it's a fine cast, but on Monday it was lacking, apart from Felicity Lott's sumptuously poignant Countess. Thomas Allen was in poor voice; Randi Stene's Cherubino had intonation problems; Andrea Rost's Susanna didn't blossom until the last act; and although Gerald Finley's lithe, young, feisty Figaro had quality, it didn't displace the memory of Bryn Terfel last time round. Bernard Haitink conducted with conscientious sloth.

It may sound an unrealistic comparison but, staying with Mozart, I got more enjoyment from the Cosi fan tutte which a small, shoestring company, Opera Inside Out, has been running at the Corn Exchange, Newbury. If the singing wasn't Salzburg standard it was certainly competent and committed; the cut-down orchestra under Jonathan Gill played with infectious energy; the set (neo-classical with touches of Omega Workshop) astonishingly pretty; and the production, by Kevin Scott, managed a variant on the ending that struck me as original (quite a feat) and true to the piece - namely that Ferrando gets Fiordiligi, leaving Guglielmo (who doesn't want Dorabella) and Dorabella (who wouldn't mind Guglielmo if she only had the chance) painfully adrift.

Finally, a note on The Juniper Tree, a new chamber opera by Andrew Toovey presented by Broomhill. Remembering Toovey's last opera, Ubu, I went to it with low expectations and was surprised to find a strong, persuasive piece of music theatre, memorably staged by Stephen Lang-ridge and happening in the oddest opera venue I've encountered: a shed behind a public lavatory in Southborough where you had to bang on a garage door for entry. It was like infiltrating an Ecstasy party; and since the door came down behind you there was no escape until the last note. Cunning.

'Nabucco': Cardiff New Theatre (01222 878879), continues Tues & Fri; 'Carmen': Coliseum, WC2 (0171 632 8300), continues Tues & Sat; 'Le Nozze di Figaro': Royal Opera House, WC2 (0171 304 4000), continues Tues & Thurs.