Nation, National Theatre, London

With a good deal of theatrical fare designed for family consumption at Christmas, you can confidently check your brains in at the cloakroom and sit back expecting a certain end-of-term laxity on the artistic front. But not at the National Theatre where, if anything, the creative excellence has tended to be intensified in Yuletide-born shows such as War Horse, Coram Boy, and pre-eminently the adaptation of Philip Pullman's masterpiece, His Dark Materials.

These last two spring to mind while watching this year's effort: a stage version by Mark Ravenhill of Terry Pratchett's hit novel Nation. But I'm afraid that the comparison does not work to the advantage of the new piece. As with a strand of His Dark Materials, we are in a parallel world. It's 1860 and two teenagers are hurled together as survivors of a tsunami that has destroyed a South Pacific island village – Mau (strapping, loin-clothed Gary Carr), a native of the island, and the posh, well-connected English teenager Daphne (squeaky Emily Taaffe), who has been shipwrecked. But His Dark Materials dramatised a colossally arduous rite-of-passage into puberty whereby two 12 year olds from parallel universes embraced sexual love in a way that redemptively re-enacted the Fall. In the much shallower Nation, Mau and Daphne feel like crude counters in an exercise in politically correct sermonising about the superiority of science to religion.

Melly Still's production occasionally creates ravishing visual effects with its three large picture-framed aquaria, which swarm with scene-setting video footage or purl with blood during moments of violence.

But morally and emotionally, the drama is undernourished. The tsunami seems to cure Mau tout court of any fundamental belief in the patriarchal gods of his tribe and his rite of passage into the assumption of responsibility as adult head of his nation is insufficiently pitted with deep dilemmas. Meanwhile, irritating Daphne progresses too smoothly from patronising tea ceremonies, via queasy cultural trials that are reminiscent of I'm a Celebrity...Get Me Out of Here (a programme on which no one, as yet, has had to suck the teats of a drugged pig to secure the milk for a dying baby).

To 28 March (020 7452 3000).