“Denmark's a prison” says Hamlet and Ian Rickson’s intriguing production echoes his thoughts, except that Elsinore is now a secure psychiatric unit, where even the audience are scowled at by unsmiling wardens.

So after the brouhaha over the RSC's Marat/Sade, we’re plunged straight away into another production set within the confines of an institution with its portrayal of mental instability and family breakdown.

Of course, it's Michael Sheen's Hamlet that makes this the hottest ticket in town and he doesn't disappoint. This is a deeply troubled Prince, acting out his own father's ghost. It’s not a new idea, Jonathan Pryce did the same at the RSC, but Sheen is not possessed by his father’s spirit, he takes on another persona.

But then that is what Sheen does throughout the full three and half hours, effortlessly switching from moments of lucidity to wild-eyed lunacy. In his fevered state, "The Mousetrap" becomes, not so much a play to catch a king, but a wild, Oedipal fantasy with Gertrude centre stage and with the killing banished almost to the background.

There are several strong performances to support Sheen's portrayal. James Clyde's Claudius, a suave Bryan Ferry lookalike, all-powerful psychiatrist alternatively drugs and patronises his patients. Vinette Robinson is a powerful Ophelia, disintegrating completely after her father's death, dispensing drugs in place of flowers in a grotesque parody of the psychiatric treatment and Michael Gould fussily obsessive Polonius, with his perpetual Dictaphone were also strong portrayals.

Jeremy Herbert's design (starting from outside the theatre, the audience approach their seats from backstage) is a superb, eerily accurate depiction of a secure unit.

But despite Rickson’s vision and Sheen’s compelling performance, there’s something missing. Just how mad is Hamlet is one of the central questions of the play and by deciding his mental state from the outset loses some of that subtlety. And taking away the political dimension offered by the always-present threat of Fortinbras loses a central tenet of the play.

There are also some unexplained moments - if the Ghost was a figment of Hamlet's mind, how do Bernardo and Horatio see him? And how does Hamlet know the details of his father's death without supernatural intervention? Someone coming to the play for the first time would probably leave the theatre rather confused.

It’s a pity that such quibbles detract from the strength of Sheen’s portrayal. It may not be the most assured production, but the central performance will be remembered for some time to come.

- Maxwell Cooter