Opera: Mathis der Maler Royal Opera House, London

'I don't think I've ever seen Sellars's work so spare, so focused, so involved'

Of the many questions posed and pondered in the course of this extraordinary evening, only one may finally be answered with any certainty. That Hindemith's Mathis der Maler is indeed one of the great unsung pieces of our time. I hesitate to use the word "masterpiece" because masterpiece implies perfection and perfect Mathis is not. Mathis outreaches itself. It is a work of conscience teetering on the brink of self-indulgence - but it dares. It dares to ask the awkward questions. What is the artist's responsibility? What function can he serve in a world threatened by social, political, moral bankruptcy, a world where dog eats dog, where injustice is met with revenge, where a divided church offers only platitudes and dead saints, where that which does not conform is expendable?

Mathis is, of course, autobiographical. It is Hindemith's "dark night of the soul" as surely as it is his painter hero's. It is about learning to be a man before seeking fulfilment as an artist. The Nazis had assumed power in Germany; Hindemith had seen the future. To what extent was he, the artist, a part of it? So this was his odyssey. History has a nasty habit of repeating itself. Even as he devised his 16th-century scenario, he was doubtless thinking 21st century.

Which is where Peter Sellars, the uncrowned king of urban angst, comes in. It was both a risk and an inspiration assigning this production to him. Sellars is the kind of director who likes to change the world. No one brings more personal baggage to his work, no one is more fixated on the machinations of the extreme Right as he is. He is truly a child of the American Nightmare. And we know to our cost that he can get in the way. But not here. I don't think I've ever seen his work so spare, so focused, so involved.

As we enter the theatre, we enter a no-go zone. George Tsypin's set, tilted precariously in post-riot, post-terrorist-bomb limbo, is cordoned off from the auditorium. It is a dangerous environment - singers venture where angels fear to tread. An extension platform-ladder - looking like a makeshift pulpit - has torn through a section of skyscraper (like a kind of inner-city stigmata).

Mathis soliloquises about how his sabbatical year among the monks of St Anthony has changed his life. As he tries to make sense of his thoughts, his words are mirrored in the mime, or "signing", of an actor/dancer (Michael Daniels). So straightway Sellars has found a dramatic metaphor for his man of vision, a way of expressing the visual, the imagined, in physical terms. The painter's viewpoint. Developed into a kind of physical leitmotif for the entire staging, it becomes an extraordinarily poetic adjunct to the agony and ecstasy of Hindemith's epic score.

That score seems to burgeon in our imaginations from the three exalted tableaux we know as the Mathis der Maler Symphony - the wonder is that so much of it maintains that level of conviction. Rarely is Hindemith guilty of falling back on what one might call the greyness of his academic counterpoint. Mathis burns with integrity - and, the tentative chordings of the prelude apart, the Royal Opera Orchestra responded to Esa-Pekka Salonen's fervour like true believers. So, too, a cast so plainly committed to Hindemith's, to Sellars's vision. Reaching out to each other across a darkening divide, Alan Titus's resounding Mathis and Inga Nielsen's Ursula were performances - presences - of extraordinary intensity. Nielsen is a singer whose big notes are wrenched from somewhere deep inside. Courageous, unforgettable. You know when something special is happening in the theatre. Perhaps Mathis's time has come. Perhaps, like time, it's a natural healer.