FOR NEARLY half a century the ritual response to Michael Tippett's ritualistic opera The Midsummer Marriage has been "magnificent but inexplicable" - and from the conversation in the coats queue after Covent Garden's new production on Tuesday it was clear that not much has changed. In fact, the coats queue could have been rehearsing the famous feature that appeared in the News Chronicle when Covent Garden first staged Midsummer Marriage back in 1955. Under the headline "This opera baffles us too, say singers", a young Joan Sutherland was quoted saying, "Mr Tippett told me not to worry if I didn't understand it. He said just to sing it as well as I could and to leave the audience to work out the significance for themselves." Meanwhile Tippett, on the same page, offered the advice: "It means what it says" - which is the sort of loftily unhelpful comment T S Eliot used to give bewildered readers of The Waste Land.

But then Tippett always did take his cues from Eliot; and Midsummer Marriage comes so close in tone, texture and the way it privatises public myths to a "Waste Land with music" that you can only wonder the composer didn't publish it with literary footnotes. No libretto in the repertory is more allusive; and even when you've tracked down its references to Jung, George Bernard Shaw, Greek tragi-comedy, The Golden Bough, Mozart and Wagner, the suspicion sticks that half the detail is perversely meaningless. I've always thought there was an element of genial fraud in Tippett's intellectual pretensions.

But that said, half a century has filtered out what matters from what doesn't in the piece, and its essentials now seem clear enough. In much the same way as the later Tippett operas, Midsummer Marriage is a psycho- drama: a quest for healing and wholeness pursued through the metaphor of a pair of lovers who, like those in Mozart's Magic Flute, must find them- selves before they truly find each other. "Finding" for these purposes involves a reconciliation of the corresponding opposites that underlie existence: male and female, light and shadow, spirit and substance, rationality and instinct. And looking back, it isn't hard to relate this abstract, Jungian preoccupation with the search for wholeness and self-knowledge to the concrete circumstances of Tippett's life in the Forties and Fifties, when he was writing the opera (libretto as well as music). At a personal level, here was a homosexual composer still tending the wounds that straight societies habitually inflict on gay men. More generally, here was a creative artist working in a broken world still suffering the fallout from a major war. No wonder healing featured high on his agenda.

The strength of Graham Vick's production at the Garden is that it draws all this through much the same filter as the passing years, focusing on the essentials and gently smothering the nonsense. The set (Paul Brown) is surreal, like a spongily soft-lit Magritte, and presents the whole action as a sort of tear in the fab- ric of reality. Three hours of music-theatre become what Eliot might have called a moment in time but not of time - which I'm sure is what Tippett intended, although in the process his idea of representing the spirit- elements of the drama in Hellenic terms, complete with ruined temples and extra-terrestrials in togas, goes out of the window. Instead, things are simplified down to two abstracted objets that command the stage: a sphere (serving as a temple) and a spiral staircase (providing access up to heaven and down to hell). Behind them, writ large, are the words "I am the child of earth and starry heaven"; and in that sentence (taken from an ancient funeral tablet and used by Tippett as a preface to his score) you have the core message of the opera. A statement of the reconciled at-oneness Tippett and his mentor Jung would have us all aspire to.

Some might feel that Vick's streamlined approach has also undermined the opera's magic; but for me he merely substitutes a different kind of wonder, and I love the way he de-togas the ETs and reclassifies them as Joycean leprechauns in Paul Smith suits and bare feet. I also love Ron Howell's vitamin-enriched, exhilarating DV8-ish choreography (the ETs are essentially dancing roles) and the way the central dancing role of Strephon (wonderfully done by Stephen Kirkham) comes through with a sympathy and characterfulness I'd never have imagined from years of listening to Midsummer Marriage on record.

The singing, too, is impressive, with a cast dominated by John Tomlinson as King Fisher, the bullish businessman father who tries to stop the wedding, and embellished by Cheryl Barker in the coloratura female-lover role, Jenifer, originally sung by Sutherland. Stephen O'Mara as Mark, the male lover, is slightly disappointing: a small, closed voice without the richness to exploit the generosity of Tippett's lyric writing. But Christopher Ventris and Lilian Watson as Jack and Bela - the comic servant/ soubrette counterparts to Mark and Jenifer - are a joy: Ventris is especially commendable as a young talent that's really coming on well.

As for the conducting, Midsummer Marriage isn't natural, instinctive repertory for Bernard Haitink, in the way it is for somebody like Colin Davis. The ecstatic utterances of the orchestra don't sing enough or get the space, the rapture, the indulgence they demand. It's all slightly repressed. But Haitink does appreciate the need to treat the score like Wagner, with sustained lines and a sense of architecture; and in any event, this is music of such irrepressibly exultant splendour that it can hardly fail to work. The best of Midsummer Marriage counts among the best operatic writing of this century; and even if its beauty sometimes feels contrived rather than pure - the product of elaborate mechanisms rather than direct simplicity - it's still a fabulous, exotic beauty that saturates the senses with abundance. I don't pretend to any special understanding of the chemistry of aural intake, but I know that the chemistry of Midsummer Marriage is profoundly powerful; and when I hear Mark's first-act aria my heart dances with the realisation of why the Barbican called its recent Tippett festival "Visions of Paradise". Now 91 and almost totally blind, the messenger of paradise shuffled tremulously on to the stage after Tuesday's performance, and the entire house leapt to its feet: not necessarily comprehending but definitely captivated.

'Midsummer Marriage': ROH, WC2 (0171 304 4000), continues Sat.