The mystery of what is wrong with Ivanov the play - why it is so rarely performed and frequently critically dismissed - is less easily answered. In Michael Grandage's fluent, humorous, humane production, there appears to be nothing wrong with it at all. The revival of Chekhov's first full-length play is an unreserved triumph. Much of the credit must also go to its adaptor, Tom Stoppard, who has clearly left it in better shape than when Chekhov finally put down his pen and abandoned his rewrites after a disastrous premiere at the Korsh Theatre in Moscow. Mind you, it will also have helped that the Donmar's starry cast were not drunk, the condition of some of their predecessors in 1887.

Here in this early work, Chekhov is already proving himself the great dramatist of boredom. In this provincial community the families and hangers-on of Ivanov and Pasha cope with their banal lives in a finite number of ways: gossip, card playing, fireworks, vodka drinking and romantic intrigues. Above all there is cynicism: Pasha (Kevin R McNally) and Ivanov's uncle the Count (Malcolm Sinclair) compete with Ivanov for the title of top misanthropist. Ivanov's hatred, however, has turned malignant and is destroying not only him but those around him.

Particularly he stands accused of killing his wife, the tubercular Anna, played with luminous forbearance by the excellent Gina McKee. Ivanov's egotism, self-indulgence and selfishness are beyond irritating, and his treatment of Anna is by any standards disgraceful. She faints when she spots him in an embrace with Pasha's teenaged daughter Sasha. Later he calls her a "silly Yid" and "a dead woman" - the first she has heard of the doctor's gloomy but accurate prognosis. This, he confesses, is the worst thing he has done; yet within a year or so Anna is dead and he is about to marry Sasha. But Branagh lets us see why he is attractive, why Pasha and Sasha and Anna all love him. His despair is authentic and passionate. In a play in which everyone prides themselves on their candour, Ivanov's depression is the truest thing of all.

For some of Chekhov's characters, Ivanov's problem is a matter of moral failing. The on dit is that Ivanov married his "Jewess" for her parents' fortune. When they disowned her and their money did not appear, he set about betraying her and looking for a new honeypot, in this case Sasha (the West End's new bright hope, Andrea Riseborough).

A young, infatuated doctor is particularly sure of himself on this score but his judgementalism is the most callow thing of all. As Ivanov says to him, in a speech that recalls Hamlet's speech to Rosencrantz and Guildenstern ("You would pluck out the heart of my mystery"): "What a simple machine is man. But there are too many cogs and springs and wheels within wheels for such easy judgements."

The ghost of Hamlet lies like a palimpsest on this play, but only for us to see how hard it is for a real-life Prince of Denmark to achieve tragic dignity. Ivanov warns Sasha that she finds herself as Ophelia in a "provincial performance of a hand-me-down Hamlet and his awestruck disciple". Earlier he has told her that his dilemma is the "stuff of comedy and nothing more". It was Chekhov's genius, and now Grandage and Stoppard's, to let us see how there is more to life than comedy, even if it rarely reaches the zenith of tragedy. The play, as performed, is cruelly funny but also serious about people who find it hard to be serious about themselves.

The end duly shocks even if it prefigures the pay-off to The Seagull. Pasha and Ivanov's nostalgia for their university days in Moscow predicts the Muscovite yearning of the three sisters. Uncle Vanya features a more interesting doctor. Yet this is a mature play in its own right, and a tremendous night at the theatre.