Opera Premiere: Ines de Castro; Edinburgh Festival Theatre

James MacMillan has dedicated his new opera, Ines de Castro, to the memory of Sir Alexander Gibson, who founded Scottish Opera in 1962 and whose conducting inspired the composer as a boy. Friday's world premiere showed off a company on splendid form: in particular, the orchestra under Richard Armstrong gave a remarkable account of the lurid, fiercely exigent score. There were particularly vivid passages for percussion (including a xylophone hit with a hammer) and bass clarinet. MacMillan also combines instruments for colouristic effects: cellos and double-basses accompany the king's debate with his evil counsellor, Pacheco, a scene reminiscent of Verdi's Don Carlos.

There's the rub. Conceived on a grand scale, in response to great works by such as Verdi, Wagner and Puccini, Ines de Castro is, however, James MacMillan's first full-length opera. It's his Oberto, his Liebesverbot, his Edgar. Like a precociously ambitious child, it can't help showing off everything the composer can do, as well as several things he can't. It opens on home territory, with a Stabat Mater and religious procession, but the soprano's first aria never transcends John Clifford's indigestible, wordy text. The cast articulate conscientiously; perhaps fortunately, many of the words are buried in a relentless sequence of loud, violent climaxes - probably no more was lost than in Janacek.

Reading the libretto (published by Boosey and Hawkes) exposes its sentimentality. Despite the radiant presence of Helen Field in the title role, we never care for Ines, either living ("I want to see people greet each other with extravagant embraces and cries of delighted surprise") or dead - when she attends her own skeleton's coronation and misleads one of those little girls that litter opera's final scenes ("They'll tell you that they have to kill, that they cannot avoid committing crimes. Do not believe them"), over twinkling harp and celesta.

Jeffrey Lawton sings heroically as her lover, Pedro; Stafford Dean lends his majesty to the role of the king; and Jacek Strauch breathes life into the cliched character of Pacheco: he wears a lot of leather, grabs a pair of Ines's bloomers off a clothes-line and sniffs them; that's how wicked he is. Anne Collins does a nurse number but is even better as Death, while Elizabeth Byrne sings like an angel in the role of Blanca, Pedro's wronged wife. Christopher Purves scores a hit as the executioner, taking us through Pacheco's death by torture with the aid of a diagram (it involved heated pitch - "a drop in every orifice" - and proved all too audible).

Jonathan Moore's production can be very portentous (slow walks and extras doing what the soloists sing about, as if acting could be delegated) and indulges in feeble comedy (Ordinary People in unfunny commedia routines). The straightforward designs of louring columns are by Chris Dyer and the atmospheric lighting by Paule Constable.

On a first hearing, the best that can be said of the piece is that Scottish Opera are to be congratulated for wholeheartedly helping a promising young composer to develop. Roll on Mr MacMillan's later work.

In rep at the Theatre Royal, Glasgow, from 25 Oct (booking: 0141-332 9000) and touring to Edinburgh and Newcastle in late November

ANTONY PEATTIE