The Mariinsky Ballet, Sadler's Wells, London

At the end of a dull evening, the dancers of the Mariinsky (formerly Kirov) Ballet come to life in William Forsythe's In the Middle, Somewhat Elevated. Stretching a foot, as if testing her pointe shoes, Ekaterina Kondaurova looks sleek and fierce, eager to take on these steps.

For the first time, the Mariinsky Ballet is appearing at Sadler's Wells – at a dance venue known for contemporary work, rather than an opera houses. The visit features a smaller, more flexible group of dancers, with adventurous repertory... and cheaper tickets.

Well, that's the idea. Yet the repertory isn't groundbreaking, for British audiences or even for this conservative St Petersburg company. The first all-Forsythe programme presents ballets that the company danced at Covent Garden three years ago. We have to wait for the second programme, including Alexei Ratmansky's Middle Duet, for something new. Worse, most of these performances aren't fresh. In 2005, the Mariinsky looked wildly excited by Forsythe. Three years on, they're getting complacent. Only In the Middle has kept its gloss.

Steptext, created in 1985, is a deliberately fractured dance. A recording of Bach's Chaconne stops and starts, lights go on and off in the auditorium, dancers stroll away from the middle of their solos. Ekaterina Konadurova, a redhead in a red leotard, throws her legs into drastically high extensions, but looks dry and mannered. The whole performance needs more bite.

Approximate Sonata has gone off the boil. Andrey Ivanov inches forward, contorting his face to match the roars on the soundtrack. Different couples break into arguments, in Russian, about how the steps should go. There's a little more energy in The Vertiginous Thrill of Exactitude: the frantic speed of the choreography demands it. Forsythe plays with the classical tradition, with academic steps. It's an airless, self-conscious take on the past. Forsythe's phrasing is choppy and his pointework stomping or hectic.

In the Middle saves the night. To the clunks and thuds of Thom Willems's score, the dancers slice through Forsythe's walloping moves. For the first time, the dancing has real scale. Irina Golub's duet with Mikhail Lobukhin has a sharp-edged precision. In the other leading role, Kondaurova dances with triumphant glamour. When she slams her long legs into extreme poses, it looks like a dance of victory.

Season continues until tonight (0844 412 4300); The Sadler's Wells Forsythe in Focus season continues until April 2009