DANCE Sylvia Opera Garnier, Paris Sleepers Guts Chatelet, Paris

Who, somebody once asked, is Sylvia? What is she? In ballet, she is a favourite nymph of Diana, goddess of the chase and the chaste. Eros rescued her from nasty Orion for a happy ending with nice Aminta. Delibes wrote for her one of the best of all pre-Stravinsky ballet scores, and for the French she is special because her ballet was the first commissioned for the magnificent Opera Garnier.

Nearly 20 years after the last revival there, it was high time for another, and received opinion is that the last one was not successful (although I remember it as having many merits but a dreadful decor that could have been replaced). So what better than to ask John Neumeier - almost the last good classical choreographer left in Europe, and one renowned for finding new readings of old subjects - for a new version?

Unfortunately, this time he has been too clever by half. Wanting to avoid what he thinks is the kitschness of earlier versions, he has embroiled himself in classical mythology and a psychological interpretation that parallels Sylvia's love for Aminta with Diana's for Endymion. Imagine, a leading character fated to sleep eternally! Neumeier handles this ingeniously, with sleepwalking slowness, and doesn't cheat too much even in the somnolent pas de deux, but it is more than a little limiting.

In fact, his post-modernist treatment proves more kitsch (and a lot less charming) than what it replaces. Yannis Kokkos's sparse, handsome decor and bizarre, uglifying costumes take the action from antique groves to a stark contemporary museum where gods in dungarees and huntresses in white knickers with leather trousers mingle with shepherds in woolly pullovers and party guests in elegant long dresses or black tie.

So do the music and the dancing save the day? The dancers, yes, even if the second-cast Sylvia and Aminta, Fanny Gaida and Nicholas Le Riche, prove more touching than their more soigne equivalents, Monique Loudieres and Manuel Legris, on opening night - but then one loses Le Riche's wonderfully funny and sexy Eros from the first team.

What they all have to do is beautifully done, but not itself beautiful. Neumeier, who directs the Hamburg Ballet, seems to have caught a tendency to jerky head, hand or hip movements, and bent knees, from a recent guest choreographer there, Mats Ek. Somehow with this he manages to make the most fluent of Delibes' melodies sound twitchy.

Besides, he has carved up the score, replacing chunks with bits from the composer's earlier ballet La Source. If he did not like the music (in a programme note he refers sniffily to an "operetta side" to it), why take on the job? Happily, the orchestra under Vello Pahn take it more seriously. A joy to hear.

Neumeier is not the only American choreographer in Paris this week. William Forsythe's Frankfurt Ballet at the Chatelet has a new work, Sleepers Guts, a characteristic mix of highly original movement sequences and bold theatricality, powered by the driving score of Thom Willems and Joel Ryan. Much talk and dressing up, plus many projections, vie with unusual dance ceremonies in the first half; but the almost all-dancing second and third parts, including Jacob Godant's long, aggressive duet for himself and Ander Zabala, are thrilling.

Forsythe and Frankfurt suggest a future for modern ballet. Neumeier and Paris have taken a dead-end bypath. But both will soon find other routes. And having rediscovered this music, the Ballet de l'Opera should have another go at it before too long. Ashton's version is better, for instance; or why not let Pierre Lacoste, a specialist in old styles, reconstruct the ballet from traditional sources?