The Sacrifice, Wales Millennium Centre, Cardiff<br/>The Shops, Linbury Studio, London<br/>Mahler's Third Symphony/Gergiev, Barbican Hall, London

Ten years in the making, James MacMillan's grimly powerful new opera was surprisingly warmly received

Visions of the future have always revealed the anxieties of the eras in which they were created. So too, The Sacrifice, commissioned by Welsh National Opera and developed over a 10-year period by the composer James MacMillan, librettist Michael Symmons Roberts and director Katie Mitchell. Adapted from The Mabinogion, the opera is set in an unnamed country, 70 years in the future. The world has run out of oil, its warring elite live in shell-scuffed hotels, a dynastic marriage is their only peace initiative, and cries of "Shalom!", "Salaam!", "Heddwch!" and "Salve Regina!" have replaced the traditional nuptial toasts.

As befits the burn-out scenario, there's a lot of smoking in The Sacrifice, a lot of illicit grappling in hotel rooms, a lot of lurking in darkened corridors, and a lot of violence. But the smoking is notably unenthusiastic, as is the grappling that sees hot-tempered Evan (Leigh Melrose) cling to long-suffering Sian (Lisa Milne) like a lonely seal on a rocky outcrop. Still, the lurking is effective and the violence is impactful. For Sian is not the only sacrifice in this glum drama. Also sacrificed are seven-year-old Gwyn (Cameron Jones), the first-born son of Sian's enforced marriage to Mal (Peter Hoare), and the General (Christopher Purves), former adversary of Mal and father to Sian.

Though The Sacrifice concludes with a passionate call for peace from twice-bereaved Sian, the outlook after several hours of kiss-kiss bang-bang is bleak. Yet the applause at the end was as warm as any I've heard for a new commission. For MacMillan has created a modern opera for people who dislike modern opera, with an extended love duet ("Skin is border country"), a touching aria for a proud father ("Seven years ago"), a moving lament for a grieving mother ("I thought my hands were heaven blest"), rousing set pieces for the chorus, scoring that respects the tessiturae of voices and instruments, and music that we have been programmed by Shostakovich (the plaint for violin and flute), Wagner (the hammering of the anvil), and Britten (the trilling of Sian's female attendants) to associate with particular emotions.

If Symmons Roberts' libretto jumps awkwardly from poetic to demotic, there is nothing to confuse the listener. Equally plain are Vicki Mortimer's set designs, a banqueting hall redolent of Bosnia, its exterior hinting at the World Trade Center in stark concrete verticals. And for audiences used to Mitchell's work, there are more familiar tropes: a dead child to represent despair, a living one (Mal and Sian's second son) to represent hope, a holy innocent (Sarah Tynan as crazy, gentle Megan), an impotent patriarch (Purves) wracked with grief, and a community's unease manifested in tiny individual movements.

WNO's principals sing powerfully, with Milne radiant in Sian's long laments and her trio of attendants Amanda Baldwin, Rosie Hay and Samantha Hay beautifully blended, while the chorus and orchestra give this old/new score immediacy under MacMillan's beat. Few operas enjoy premieres as well-executed as this.

Where MacMillan's gift is for tragedy, his former pupil Edward Rushton has a talent for comedy. But The Shops, an absurdist romp about a kleptomaniac philatelist and his shopaholic sidekick, puts music so much at the service of words that Rushton's score was in danger of disappearing in a tiny puff of ice, like a Heston Blumenthal palate cleanser. Excepting Act I's waspish trio and the snappy little sextet in Act II, the 10-piece orchestra of strings, clarinets and percussion was used more as lighting design than accompaniment: lending a glint or gleam of colour to this or that one-liner, steering the singers through several breakneck flash-backs, and suspending the narrative on a thin wire of windchimes while The Opera Group's cast of six stepped out of character to read aloud a letter from librettist Dagny Gioulami.

It's tempting to dub Gioulami the Candace Bushnell of opera. But the observational humour gleaned from a thousand humiliating expeditions to designer boutiques – "No, we only have up to size 8!" – is balanced with a tenderness that Sex and the City rarely demonstrated. When not dabbling with Kafkaesque fantasy or No Logo politics, Gioulami is admirably sympathetic to the geeks of this world: the policeman (Oliver Simons) rattled by the psychologist's superior salary, the psychologist (Louise Mott) whose art-market investments are perhaps emotionally inspired, the retired journalist and active bore (Paul Reeves), the compulsive thief (Darren Abrahams), his wounded mother (Phyllis Cannan), and his girlfriend Francesca (Anna Dennis), whose clothes look lovely in the store and unlovely at home. With terrific performances from all six singers in John Fulljames's perfectly paced production, and ingenious designs on the theme of carrier bags by Soutra Gilmour, The Shops was as guiltily and briefly pleasurable as spending too much on something you don't really need.

Briefly pleasurable too, was Valery Gergiev's performance of Mahler's Third Symphony, first of a complete cycle with the London Symphony Orchestra. For the duration of the vast first movement, Gergiev reinvented this Central European symphony in the mould of Eastern Europe, producing a narrative of epic emotionalism and lurid, bloody colour. Though known for his fortissimi, Gergiev's pianississimi were equally startling, with ghostly whispers of strings, sickly flickers from the woodwind, glancing, dancing solos from leader Carmine Lauri, sensational work from the timpani, and a languid solo from trombonist Dudley Bright. Unfortunately, what the meadow flowers, forest animals, morning bells, and love allegedly told Mahler about life in movements two to six became increasingly difficult to comprehend in Gergiev's idiosyncratic translation, and the architecture of the symphony was rapidly destabilised. For the opening movement, this performance was unforgettable. The rest, I hope, will fade.

'The Sacrifice' (0870 040 2000) to Sat; 'The Shops', Royal Northern College of Music, Manchester (0161 907 5555), Thurs; Oxford Playhouse (01865 305305), 7 Oct

Need to know

JAMES MACMILLAN took the plot of 'The Sacrifice', his second opera, from 'The Mabinogion' – a collection of prose stories from medieval Welsh manuscripts which are based partly on early medieval events, but which also draw on Iron Age narrative tradition. His first opera, 'Ines de Castro' (1996), dealt with the murder of the lover of King Peter I of Portugal and premiered six years after MacMillan's first international success, at the Proms, with 'The Confession of Isobel Gowdie'.

This week Anna Picard read Ariel Levy's Female Chauvinist Pigs: Women and the Rise of Raunch Culture: 'hilarious and disturbing'. She watched The Wire, a drama series about the Baltimore drugs trade: 'gripping, though they speak such heavy patois I only get about one word in five'

Further reading Sioned Davies's new translation of 'The Mabinogion' (Oxford World's Classics)