Ondine, Royal Opera House, London

Frederick Ashton's 1958 ballet, Ondine, the tale of a water sprite's love for an unfaithful prince, was old-fashioned even when it was new. It has an enchanting ballerina role, created for Margot Fonteyn, but surrounds it with an awful lot of padding. Ashton's watery imagery goes from poetic to kitsch and back again. Lila de Nobili's designs include mistily evocative landscapes, but unflattering wigs and boots.

Ondine needs a strong performance to cover its weaknesses. This Royal Ballet revival has improved since last year: the company dancing is tidier, though the corps scenes still lack impact.

A lot rests on the ballerina. To general surprise, Alexandra Ansanelli has just announced her retirement from ballet. Still in her 20s, she's chic but not always strong. Having started her career with New York City Ballet, she moved to the Royal in 2006, for the sake of its repertory of classic and dramatic works.

In fact, the drama of Ondine suits her best. She's underpowered in the first act: her wrists too fussy, her feet not articulated enough for the rippling qualities of Ashton's dances. With the second act, as Ondine and her lover Palemon travel by ship, Ansanelli's heroine wakes up. She's flirty and fey – pouting when he ignores her, eagerly skipping from one new sight to the next. When she leans over the side, her playing with the waves is beautifully casual: doodling gently to herself, Ondine doesn't notice that she's raising a storm.

The ballet's old-fashioned quality extends to the sometimes charming stage effects. Dancers sway in unison to show the ship's motion. Returning to confront her unfaithful lover, Ondine dances in the gauze waves, held above their surface by unseen partners.

Valeri Hristov is a supportive partner, but his Palemon is too passive, pushed about by the plot and the women in his life. As Berta, Ondine's jealous rival, Laura Morera manages to turn a plot-device character into a believable person. She's vulnerable when looking for her lost lover, angry but understandable when reacting against Ondine. Her steps are bright and hard, furiously gleeful.

Hans Werner Henze's score for Ondine has always been a sticking point. Audiences, and indeed the choreographer, found Henze's washes of sound hard work, but Barry Wordsworth's conducting balances lushness and texture with a driving sense of momentum.

In repertory to 6 June (020-7304 4000)