As You Like It, Wyndhams Theatre, London

This must be the first production of As You Like It where media coverage has focused on the actress playing the secondary female role. But Celia is played here by Jude Law's 23-year-old fiancée, Sienna Miller, who brings all the professional experience mustered from appearing in three movies.

For the privilege of losing her theatrical virginity in a plum Shakespearean part, she has had to wrestle with terrible handicaps. Her husband-to-be is the celebrity figurehead of the Young Vic's rebuilding campaign. This As You Like It is a Young Vic co-production, directed by its artistic chief, David Lan. Other actresses might have crumbled. Not Miller. The question is: having shown her mettle off stage, how does she shape up on?

Well, let's put it this way - I once saw a 13-year-old girl give a subtler and more captivating performance as Celia in a school play. Limited to a gratingly narrow range of gestures and expressions, and the victim of inadequate direction and voice, the wooden Miller has to resort to the amateur's tactic - shout and exaggerate. She approaches an emotion with the finesse of someone beating a carpet.

To be fair, Miller is not alone in her incompetence. The play is relocated to 1940s France. The banished Duke Senior (Clive Rowe) and his courtiers appear to be a group of exiled musicians, who regale the forest with sophisticated Gallic melancholy and occasionally double (using umbrella handles for horns) as the pastoral flocks. The gags and bits of business (having Rosalind, say, read from the footnotes to the Arden edition in the epilogue) have an extraneous, anxious feel, betraying the absence of any coherent imaginative vision of the piece.

The stand-up comedian Sean Hughes offers a flaccid, sanitised take on the fool Touchstone and fails to suggest his slippery relativism. As Jaques, Reece Shearsmith (of The League of Gentleman) is a stroppy non-entity instead of a self-absorbed and philosophical cynic. His "seven ages of man" speech has been shifted so that its pessimism about the end of life is no longer pointedly belied by the entrance of Old Adam, tenderly supported by Orlando. Equally, it's not a smart idea to have the pairs of lovers in the finale cheesily upstaged by a singing, campy, green-suited Hymen (Nigel Richards). The kitsch drowns out the magic.

Helen McCrory, who is in a different league from most of her colleagues, manages some witty, touching oscillations between mannish bravado and vulnerability as a deep-voiced, sexily suited Rosalind/Ganymede. But this As You Like It reduces even her to bouts of overacting. She and Dominic West, whose Orlando is appealingly rugged and damaged, at times communicate the need and tremors of sexual ambiguity in this odd courtship. To excel, though, they would need to be in a production with deeper roots than those shallowly planted here.

Booking to 3 September (0870 060 6633)