Patrick Marber has fashioned a ravishing, thoroughly modern make-over for the worst sex-addict in theatrical history, Moleière's Don Juan. The humour and witty invective is imaginatively cruel, even sufficient to pleasure practising sadists.

Rhys Ifans, resembling the young Peter O'Toole, makes a dazzlingly arrogant impression as the lordly DJ, too languid to put a cigarette in his own mouth, or light it, and equipped with a monstrous ego.

"Down with selfishness and up with me, " ironically announces this haughty, priapic seducer, who styles himself the "Kofi Annan of Copulation", on a mission to rescue sexdeprived females.

The scene is mainly set in a cheaply glamorous hotel with garden-gnome stools. Here DJ laps up ladies and tarts alike with all the fervour of a thoroughbred cat dipping into the cream.

One hilarious scene in a hospital slips easily into sexual farce and revels in the seducer's shameless opportunism. Masquerading as a doctor, DJ feels up a female patient who fellates him under cover of a blanket, while he chats up the woman beside them.

Marber's intention is surely to portray DJ, Marber's name for Don Juan, as one of those contemporary-aristocrats who believe themselves well above the moral or societal laws of civilised behaviour. So, as in the original, DJ remorselessly screws himself into an early coffin, thanks to that agent of Nemesis, the Statue. In Christopher Oram's persuasive design, this statue dominates the stage as a giant, ghostly figure, with a face that moves, sepulchral voice and a role as a cyclerickshaw driver leading the impenitent lecher to death.

Purists and pedants may resent the way Marber has taken almost as many liberties with Molière's text as Don Juan took with those gullible women to whom he promised love but abandoned after the orgasm. Marber, though, offers the subtitle "after Molière" as well as the allusion to Soho, making it clear that though he follows the narrative outlines of Don Juan, his treatment is a radical rewrite, shaping the original into a modern morality or fairy tale.

In the 17th century Molière's hypocritical, godless Don Juan was condemned as atheistic. Marber's twist for our own secular times is not to make DJ admit the ceaseless itch of his sex-addiction, but to reveal him as a champion hypocrite in a world where hypocrisy has become all the rage - from political leaders who go to war proclaiming themselves saviours to a host of people making fake confessions in the media, diaries on the web and podcasts.

DJ's own show of hypocritical repentance to his father (David Ryall's nicely aristocratic Earl) is done with terrific, tearful authenticity by Ifans. It is therefore surprising that when the statue/rickshaw driver takes DJ to a place where the vengeful Irish brothers of his discarded, relief-worker wife, Elvira (Laura Pyper) threaten to murder him, he refuses to pretend repentance.

In fact, the death-bringing role of the statue strikes me as unconvincingly grafted on to Marber's text from Molière's. Better that DJ should end up still leching.

Michael Grandage's production achieves the right, frantic comic momentum, though the climactic scene lacks the nightmare sound- scape Marber required and the rickshaw fails to move. In a flash of sexual timidity, also, Grandage has removed Marber's apt allusion to DJ's gay proclivities, when no females came to hand. Still, Marber's lovely, black comedy Don Juan quite displaces Molière's.