After a lengthy world tour, Trevor Nunn's much-discussed King Lear comes home. The New London Theatre is in some ways a perfect final venue for the play; behind the theatre's concrete austerity is a cavernous space that allows Shakespeare's words to echo, reverberate and resonate.

The audience are forced into hushed reverence by the sonorous organ music introducing the first scene. Ian McKellen soon appears as Lear. Initially, he seems kindly, wise but frail. It's not surprising he's abdicating his throne; in some ways it seems sensible. Suddenly, we're thrown by the shocking violence of the decisions to banish his precious daughter, Cordelia (Romola Gorai), and his most loyal servant, the Earl of Kent (Jonathan Hyde). We realise we have misjudged him, and soon realise it is not our place to judge; this man is losing his mind. Lear casts himself out into the wilderness with only his Fool (Sylvester McCoy) for company, and succumbs, painfully, to his madness.

With the possible exception of Hamlet, this is the playwright's most psychologically rich play; its capricious ambiguities, its interpretable shades of darkness are putty in the careful hands of the right director. For the adaptation to be a success, the director must concentrate on just one of many of Shakespeare's threads, to avoid being scattershot. A strength of Nunn's version is that it has a definite direction. It aims to capture the cruelty of old age and mental decline. McKellen works hard to present Lear as a man who once had great dignity, but now finds it slipping away. As Nunn sees it, the real tragedy of the play is what old age does to you, and what it does to the people you care about.

However, the production's fault is that it does tend to guild the lily. We don't need the fate of the fool to be literally shown. Neither do we need the occasionally intrusive music. Also, however well done, the production design seems perhaps a little obvious. Although Nunn's dynamic direction can produce theatrical fireworks, too often his decisions are heavy-handed.

The delights of the evening come from the peerless performances. Hyde and Barber impress, while McCoy delivers a wonderfully memorable, and unexpectedly complex, Fool. However, predictably, it is McKellen's show. Although imbued with subtlety, his majesty comes in understanding the play's fundamental tragedy; there is enough gravitas to make the audience believe the man was once great, and enough vulnerability for you to see how far he has fallen. It's a defining portrayal. The play continues until January 12 at the New London Theatre (0870 890 0141).