The Knot Garden, Theatre Royal, Glasgow

It is fatal to live to a great age if you are an artist. It means that the junketings of your centenary come at the moment your reputation is sinking. Michael Tippett meant to be excitingly contemporary when he wrote The Knot Garden in the late Sixties, but the issues that seemed so lively then - psychoanalysis, gay liberation, the emancipation of African-Americans, political protest - now seem worn out.

The music, too, sounded modern to us at the time. Free atonality, jagged vocal lines, mixed with rock'n'roll and boogie; this was all terribly naughty and relevant. Nowadays you try not to cringe. Tippett, like Tchaikovsky, was so sincere. And sincerity, alas, dates quickest. But this composer deserves respect, too; he was genuinely humane and he went to prison for his beliefs.

It is not surprising, then, that the most believable part of The Knot Garden is the passage in Act III when the characters act out Shakespeare's Tempest. Suddenly, the opera is generous, timeless, grown-up. The scene is even funny, when the marvellous Andrew Shore, as Faber, lapses into stage cockney. The trivial engagements of the contemporary characters give way to fantasy and colour.

All considered, this production by Scottish Opera will count as one of the most important events of Tippett's centenary year. There is nothing routine about it. In a simple way, the director and designer, Antony McDonald, has evoked the claustrophobic modern household, the empty fuss of modern life, as well as the mystery of Prospero's island with its symbolic shipwreck.

Richard Armstrong, the conductor, is equally serious - too much so, perhaps, in the moments of blues and pop. The artists vary from good to excellent. Peter Savidge, as the psychoanalyst Mangus, is a poised and refined singer, but he did not dominate the way that this Prospero lookalike should. As Thea, Jane Irwin deserved praise for fluency and accuracy, though her long aria in Act III failed to gain momentum.

The gay couple - Hilton Marlton as the composer Dov, and Derrick Parker as the black writer Mel - had more flair. You didn't have to be gay to feel their tendernesses and sadnesses, their absurdities, their feelings of loss. Dov's aria in Act 2, "Come with me to the warm South", was sweet, persuasive and touching.

There are two hysterical women in this piece. The neurotic Flora, in bobbysox and Alice blue, was pictured by Rachel Nicholls as a squeaking, screaming teenager in a sort of studied panic. Rachel Hynes, lurching on crutches, was the torture-victim Denise, her long solo in Act I showing powerfully how coloratura can be used to suggest derangement.

But centenaries are the time for verdicts. So here is an interim verdict on Tippett: he was musically prodigious, but intellectually shallow. We can firm that up in 50 years, though I shall not be around to do it.

To Saturday (0141-332 9000)