His Dark Materials, National Theatre, London

At first glance, the worlds represented in Philip Pullman's trilogy of fantasy novels don't seem like easily tractable material - dark or otherwise - for the theatre. Pullman offers a multiplicity of alternative, co-existent realities, inhabited by giant, talking, armoured bears, tiny venomous warriors who go to battle astride dragonflies, angels and harpies, and, his most vivid creation, daemons - talking animals that are personifications of their owners' souls. How can flesh be put on such extraordinary creations?

At first glance, the worlds represented in Philip Pullman's trilogy of fantasy novels don't seem like easily tractable material - dark or otherwise - for the theatre. Pullman offers a multiplicity of alternative, co-existent realities, inhabited by giant, talking, armoured bears, tiny venomous warriors who go to battle astride dragonflies, angels and harpies, and, his most vivid creation, daemons - talking animals that are personifications of their owners' souls. How can flesh be put on such extraordinary creations?

As it turns out, Nicholas Hytner's production of His Dark Materials, now revived after a sell-out run earlier this year, solves these seeming problems triumphantly, catching a genuine sense of the magical. The daemons are airy constructions of cloth and wire: the major ones are manipulated by actors clad in masking black from head to toe and soon begin to take on a life of their own. Pantalaimon (manipulated and voiced by Jamie Harding) - the daemon of the heroine, Lyra - is mostly a small, fox-like creature, though children's daemons, not having found their final shape, can become moths or birds at will. He trembles with apprehension or curiosity; his tail beats the ground with pleasure; his back arches in hostility. For the bears, men in greatcoats hold aloft wire-and-paper heads - a single cable curving from the head round the actor's back suggesting cleverly the hump of the bear's shoulders.

There is ingenuity, too, in the way Giles Cadle's elaborate sets spiral up out of the Olivier's floor (though that novelty does begin to pall, it seems fair that the back-stage crew get a curtain-call of their own). And all this technical cleverness sets off a fine central performance by Elaine Symons as the wilful Lyra, a child who turns out to have the fate of entire universes on her shoulders. Symons is convincingly poised between the guttersnipe and the aristocrat; childhood and maturity. As Will, Lyra's friend from our own, daemonless universe, Michael Legge has a convincing, touchy vulnerability, though he is perhaps too much on one surly note. David Harewood is suitably charismatic and dynamic as Lord Asriel, the scientist who breaches the barriers between universes, and Lesley Manville's glamorous villainess, Mrs Coulter, balances wickedness and a streak of tenderness.

John Carlisle is a superbly slimy villain, but too many of the supporting characters are cartoonish or ill-defined. In one or two cases, the acting is at fault, but the real problem is that Nicholas Wright's adaptation - which has to condense 1,300 pages of richly textured fantasy into six hours of theatre - is not ruthless enough. It is Harry Potter syndrome: the effort to satisfy the fans by keeping in characters and incidents has led to an overcrowded, at times barely coherent, drama. Wright tries to solve the problems with passages of expository or polemical monologue, but these are frequently overlong and hard to follow.

Towards the end, the onstage tempo seems to match the action better. The journey through the underworld - part Greek myth, part medieval harrowing of hell - has a devastating eeriness. All in all, it is an admirably bold but only partly successful evening. A note for parents, though: my 10-year-old companion was riveted from first to last, and claimed to have no difficulty following the plot. You might want to take her opinion on board.

To 2 April (020-7452 3000)