Cheltenham Festival, Town Hall / Pittville Pump Room, Cheltenham

This year's Cheltenham Festival is that rare beast, an event that might tempt you actually to move in for the whole fortnight, it has so many strands, such sophistication of programming, such good atmosphere. But let's not get carried away. The programmes are fine, but the programme-book is a mess (look at the audience's average age then think how many of them need web-surfing hints), and you can't get a drink at the Pump Room, unless you call saline water, weak orange juice or instant coffee in a plastic cup drinks. Perhaps this is another of the strands, to go with Debussy, whose La Mer ended Friday's opening BBC concert in the Town Hall under Yan-Pascal Tortelier. I hope not, though; it was not a thirst-quenching kind of performance.

The Debussy theme, all the same, is intriguing, and might tell you - if you didn't know - that Michael Berkeley, the festival director, is himself a composer. Monday's Nash Ensemble concert, for instance, took its tone from L'Après-midi d'un faune in a brilliant reduction for 12 players by David Walker - better than the Eisler-Schoenberg version, with its sludgy piano and harmonium. Exquisitely played under Lionel Friend, it led the ear perfectly into the quite different lyricism of Mark-Anthony Turnage's Eulogy, an essentially linear piece for viola and eight instruments (the Debussy starts linear, with flute solo, but evolves as saturated texture, like the Tristan love music which obviously inspired it).

Debussy was also a controlling factor in Friday's late-nighter in the Pump Room. His trio sonata (flute, viola, harp) seemed to set the tone for both Simon Mawhinney's attractive if elusive Darby's Loanin, which adds oboe, and Crystallisations, by the Australian Geoffrey Palmer's, which has oboe but no harp and was actually inspired by Holst's masterly Terzetto. Holst's robust polytonal experiment, finely played by Endymion, found more of an echo, though, in the new Birtwistle Orpheus Elegies, which (because nobody knew how long they would last or how many were being played) took the concert up to midnight.

Endymion played about 15 of the elegies, and in a free order, though Birtwistle says he will fix an order when the cycle is complete. It's already a longish sit, but never less than fascinating: a kind of essence of music as language, and no nonsense about texture or sonority.

As for Brett Dean's Shadow Music in the Town Hall concert, I enjoyed its shifting blocks of sound but felt it not well served by the hall, which has its own ideas about balance. Dean, another Australian, is the festival's resident composer, and there will be more later on: another good reason, perhaps, for taking up residence oneself.