The South Bank's big idea for the autumn is a Birtwistle festival, a celebration of the composer's 70th birthday last July. Birtwistle Games is a major survey, an ambitious series of chamber and orchestral concerts climaxing with a concert performance, the London premiere, of his opera The Second Mrs Kong. But it all started in a rather subdued way, though Endymion's programme in the Purcell Room still managed to include a brace of Birtwistle premieres.

The more substantial was the first complete performance in Britain of 26 Orpheus Elegies, finished earlier this year, Birtwistle's musical response to Rilke's Sonnets to Orpheus. It's a strange, multi-faceted sequence of aphoristic pieces for oboe and harp ("postcards", Birtwistle calls them) that are really songs without words, based on the German texts. Occasionally the words break through, and so the sequence (which can be played complete or incomplete in any order, according to the performers' choice) is interleaved with settings for counter-tenor of six of the sonnets.

The work is almost a catalogue of Birtwistle's compositional techniques, his pedagogical sketchbook, and must be hard to sustain in performance. But the pieces were played with superb musicality and unswerving concentration by oboist Melinda Maxwell and harpist Helen Tunstall, though sung with less conviction by Andrew Watts.

Watts featured in the other new work, too: Three Cantata Arias that Birtwistle arranged from Bach for an ensemble with a prominent role for marimba. Claire Booth was the soprano soloist in that, but she also gave a startlingly effective performance of Birtwistle's Nenia: The Death of Orpheus, one of the earliest fruits (from 1970) of his immersion in the Orpheus myth. With its accompaniment of three bass clarinets, piano and percussion, Nenia is wonderfully concentrated, a latently operatic piece that Booth presented with more dramatic truth than any performance I've heard before.

· Birtwistle Games continues until November 11. Box office: 08700 606 096.