Sacred Monsters, Sadler's Wells, London <br/> Les Ballets Trockadero De Monte Carlo, Peacock Theatre, London

The trouble with taking liberties

Ah, star power. The Sadler's Wells autumn season has broken box-office records, and much of that can be put down to this collaboration between Sylvie Guillem and Akram Khan. In Sacred Monsters, French superballerina meets high-profile choreographer. The charisma is there, but the air is heavy with psychobabble and self-congratulation.

Now in her 40s, Guillem has been dancing a reduced ballet repertory. With this show and now as associate artist at Sadler's Wells, she takes a decisive step into contemporary dance. Khan, too, has cut between two styles. He trained in the Indian classical form Kathak, then went on to choreography (including work for Kylie Minogue's next tour).

There is dancing in Sacred Monsters, spread rather thinly over 75 minutes of vapid philosophising. It starts with Guillem holding a loop of chain, her head bowed as singer Juliette Van Peteghem wails and sighs around her. Khan steps forward to tell us that Guillem never just did as she was told. Whereupon she drops the chains, symbolising her status as free spirit.

The solo that follows, choreographed by Lin Hwai Min, gets by on personality alone. Guillem adds poise to Min's blah scoops and stretches. Her pale, narrow face is fiercely intent, while her taut, linear dancing has a reach and detail often missing from her ballet performances.

Khan tells his own story of pushing against classical restraint, before twitching into a Kathak solo. He's a superb dancer, but the effect is somehow diluted. The rhythms are simpler than in many classical solos, although his torso is still beautifully supple and free.

They show a relaxed rapport in duets, the long, lean Guillem coiling around the stockier Khan. Standing with fingers interlaced, they sweep linked arms, pulling away and springing back. She hooks her legs around his waist, and stays balanced there, as both curl and uncurl their limbs. Between dances, they tidy themselves up on stage, at ease with each other.

Both dancers have charm, authority, style. Yet Sacred Monsters is always slipping into self-indulgence, with thin choreography unfolding alongside Philip Sheppard's burbling score. Guillem and Khan complain about restrictions, while Sacred Monsters shows a loss of discipline.

Les Sylphides is full of romantic dreaming: a poet hero, ethereal women in a woodland glade. As danced by the Trocks, drag ballet extraordinaire, the effect is a little different. Ballerina Lariska Dumbchenko (played by Raffaele Morra) lands with a thud that pushes her fellow sylphs off balance. One by one, they slip down to the splits, painted faces registering woe, dismay or seething indignation.

Les Ballets Trockadero de Monte Carlo, founded in New York in 1974, truly love ballet. There's a real Sylphides going on amid the pratfalls: Lariska's jetés may thump, but her pas de chats are unexpectedly delicate. The Trocks push ballet to joyful extremes, but they never neglect its discipline.

The odd thing is that Les Sylphides is no longer performed much in Britain. The Trocks's choice can be both loyal and adventurous. Yakaterina Verbosovich and "Prince" Myshkin perform The Flames of Paris pas de deux. This Soviet rarity, coached by the Kirov-trained Elena Kunikova, was danced almost straight - even her tricolour tutu is authentic. It was sensational.

Verbosovich (Chase Johnsey) has an enviable technique. She sails through the hops on pointe, turns crisp, fast fouettés - then does the sweet head-tilts with manic exaggeration. As Myshkin, Fernando Medina-Gallego punctuates his spins and jumps with grand heroic poses.

Go For Barocco is the Trocks' salute to Balanchine, all black tunics and thrust hips - which, on this company, look downright alarming. As in so many Balanchine ballets, the corps join hands and wind through complex patterns. In Peter Anastos's choreography, you can see disaster looming from a long way off. Yet each catastrophe has its own surprises. The corps don't just get in a tangle, they do it in helplessly strict rhythm, driven into deeper trouble by the music.

Olga Supphozova (Robert Carter) gives a grand diva account of The Dying Swan, shedding several pillows' worth of feathers as he goes. His back and shoulders are stronger and more fluid than many renditions I've seen. And I love his way of striking poses of noble refinement, then sizing up the audience from beneath his thick eyelashes.

The final Raymonda's Wedding is a chance to bring on plenty of soloists, with everybody being insanely Hungarian. Kilroy Wazir (Joseph Jefferies) is a hero who barely dances, just throwing off gestures that take credit for everyone else's efforts. As so often with the Trocks, the facial responses are irresistible, from slow-on-the-uptake to instant resentment.

'Sacred Monsters', to 23 September (08707 377 737). Tours to Snape Maltings on 24 & 25 November Les Ballets Trockadero de Monte Carlo, to 30 September (08707 377 737)