Recycled myths have been the business of opera since opera began, but it was Wagner who patented their usefulness in distancing a narrative from specificity - a handy smokescreen for when complicated storylines go off the rails and stop meaning anything - and his example was taken up this week in two new operas: one of which went off the rails completely but was saved by its music, while the other went awry with a degree of charm but no salvation at all.

The first was Peter Maxwell Davies's The Doctor of Myddfai, a Welsh National commission which premiered officially in Llandudno (and before, unofficially, in Cardiff) and is a large-scale work from a composer whose stage successes have mostly been on the intimate scale of music-theatre. But recent years have seen Davies gathering stature as a symphonist; and that experience has enriched The Doctor, which progresses with symphonic tread through territorially massed ideas, meticulously plotted contours, and music that generally makes more sense than its libretto. David Pountney wrote the words - he also directs the show - and they attempt to transplant an old folk legend into a futuristically Orwellian context.

A healer from a Welsh village believes he can cure a mystery disease, unnamed but spreading like the plague, and demands an audience with the Ruler of the nightmare bureaucratic federal state the world has become. So far so good, and anyone with an agenda on Aids, nuclear fall-out or Euroscepticism will be with it all the way. But then the Doctor turns (temporarily) into a woman, seduces and infects the Ruler, and is trampled to death by a disease-ridden mob, leaving his daughter to proclaim herself the next Doctor of Myddfai and take over the world. If you can work that out, answers on a postcard please.

The one thing that sustains this non-plot is the emotional force of the score - which observes the curse of modern opera in treating the voices like a top layer of instrumental texture but packs a punch in set-piece choruses derived from Welsh hymnody and an oddly persistent sense of the music manoeuvring itself towards Leonard Bernstein without the big tunes. The 20-plus solo roles sorely tax WNO's home-team resources, but there are fine central performances from Paul Whelan (who makes a worryingly convincing woman) and Gwynne Howell. And it looks good, with a starkly chilling modernistic glamour to the sets.

By comparison, John Woolrich's In The House of Crossed Desires, which premiered at the Cheltenham Festival, is a modest piece: designed for touring, with just four voices and five instrumentalists, and playing on a single module set. But it has tried to do without too much. In the past, Woolrich's music has been distinguished by a magic fantasy quality - especially memorable in his Viola Concerto which premiered at Cheltenham last year - and this piece should have taken things further, with a libretto by Marina Warner which is all fable, fantasy and supernatural transformation. But the story fizzles out into mere cuteness, and the music is thin from start to finish, with no textural substance to support the four voices - all of them female (a perverse eschewal of pitch variety) and none of them outstanding. For a short score (two acts, 90 minutes) with a busy story, it feels very slow, the vocal writing plodding at a leaden pace. It needs remodelling: perhaps into a 60-minute single-acter, and for children rather than adults.

Otherwise, the Cheltenham Festival got off to a good start on some superbly put-together programmes which combined a Russian theme with the festival policy that every concert should feature a contemporary work. An example was the Nash Ensemble's Pump Room concert which filled a Prokofiev/ Tchaikovsky sandwich with the strikingly impressive Chaconne for solo piano by the grande dame of former Soviet composers, Sofia Gubaidulina, and the premiere of Four Primo Levi Settings by Simon Bainbridge, who writes music of such elegiac but emotionally hammering spareness that it could almost be post- mortem Shostakovich. These settings are a masterful response to the distilled pain of their texts: controlled, restrained, accompanying the voice (the mezzo Susan Bickley) with piano, clarinet and viola in autumnal colourings and quiet, reflective moods. I liked them very much.

I also liked Magnus Lindberg's dazzling orchestral essay Arena, which had its British premiere from the BBC Philharmonic in Cheltenham Town Hall. Lindberg is ubiquitous in new music programming at the moment, and this piece has already surfaced in a reduced, chamber version at the Aldeburgh Festival and at the South Bank's Meltdown. But the teeming density of the textures (each string section divisi a four) makes larger forces preferable, so long as they don't diffuse the music's energy; and this performance was ideal - exhilarating, buoyant, proving Lindberg's gift for pleasing crowds with grand gestures as well as torturing orchestras with minute complexities. Vassily Sinaisky, the BBC Phil's new Principal Guest, conducted with considerable nerve and just a touch of madness.

The best conducting of the week came from Mark Elder, who single-handedly transformed an obscure Verdi opera promising to be of academic interest into something of vitality and quasi-substance. Alzira's only claim to fame is as Verdi's least stageable stagework, and I'm not sure I'd want to see its farrago of a Peruvian Inca plot complete with feathers. But here in concert, as part of the Royal Opera's Verdi Festival, it made quite an impact: short, sharp, and an opportunity for good old-fashioned vocal histrionics which the two leads (a frontal-attack Hawaiian tenor called Keith Ikaia-Purdy and a diva-esque Chilean soprano Veronica Villarroel) didn't miss.

There was more Verdi at the Garden this week with a Traviata revival that brought together for the first time in a British theatre those two icons of operatic amour, Roberto Alagna and Angela Gheorghiu, now married and known in backstage circles as "the Ceausescus". I can't imagine why. On stage they were superb - Alagna slightly withdrawn as if yielding to the prospect that his wife would steal the show (which she did with cool, calm determination), but both in fine voice and chemically alive as characters. Thomas Allen's Germont left them plenty of space; and Simone Young's sensitive conducting kept the orchestra in support rather than competition. When you're dealing with superstars, you just have to know your place.

Garsington is not a star-struck environment - there are bigger names in the audience than on the stage - but its music director, Wasfi Kani, has a nose for talent and its new Idomeneo has a real find in Melanie Diener: a young German soprano of arresting quality who sings Ilia with such poise and assurance that it's hard to believe this is (as I'm told) her stage debut. David Fielding's Cretan-concept production and Steuart Bedford's insightful conducting make an impression, too, but this is Diener's night. The first, no doubt, of many.

'La Traviata': ROH, WC2 (0171 304 4000), to Fri. Alagna & Gheorghiu, Mon & Thurs; Kelessidi & Hvorostovsky, Tues & Fri.