Book Of Longing, Wales Millennium Centre, Cardiff

To call Philip Glass's music monotonous is a bit like calling McGonagall a minor poet: ludicrously obvious and irrelevant in the same breath. Or with the Book of Longing – Glass's 70th birthday present to himself – you might say it's like calling Leonard Cohen an ageing poet. Cohen's verse, which supplies Glass with the texts of this 95-minute song cycle, purports to be love poetry but is in fact almost entirely about fading out.

And since Cohen himself is the real subject of the performance (his morose self-portraits provide its backdrop and his pre-recorded voice cuts in with the occasional soporific epigram), the tone of the evening is, to put it mildly, valedictory.

There's a certain ghastly fascination in all this, even for those who, like me, have never quite caught on to the frisson of unmitigated tedium. Some of the poems are moderately subtle and interesting, others are more or less doggerel. But Glass treats them all much the same: the same remorseless ostinatos and Alberti basses, the same square-cut, rhyming-couplet melodies, the same moderato tempos, the same apparently studied infantilism of structure. Here and there the songs remind one of Kurt Weill. But Weill's simplicity was ironic; Glass's as straightforward as that of a child who'll get an ice cream if he asks often enough.

What redeems the performance – the work's European premiere – is the supreme stylishness with which it is presented. Glass's ensemble of four singers and eight instrumentalists (including himself on keyboard, but directed from another keyboard by Michael Riesman) has moments of stunning musicianly expertise. There are striking instrumental solos – for cello, oboe, saxophone, double-bass and a Hoffmann-esque mad violin; these are the best music and all are dispatched flawlessly. In the ensemble accompaniments the texture is transparent and glowing.

The singers, performing entirely from memory, are modestly choreographed and cunningly lit. The singing itself, in a style somewhere between opera and Broadway, is uniformly excellent, even in the quite numerous part-song settings, where one might expect such singers to have problems with blend or intonation.

All were no doubt helped by the wonderful acoustics of the (surprisingly) half-empty Millennium Centre. How they'll fare in a presumably packed Barbican when they transfer to London might be another matter – but on this showing I doubt it.