'Another Hamlet - how on earth do you cope?" asked a colleague the other day, as I set off for the National Theatre. My distinguished predecessor Philip Hope-Wallace used to encounter the same query as he trotted off to another Tosca. But, in a week when Julius Caesar and The Cherry Orchard are on the agenda, it's a perfectly valid question: how does the critic stay fresh when confronted by constantly revived works?
Hamlet, for me, is not a problem: it is too pluralistic in method, too unpindownable in meaning ever to stale. Above all, each revival offers not just a revelation of the actor's soul but a reflection of society. Take an obvious contrast. Peter Hall's 1965 Stratford production was a highly political affair in which David Warner's bescarved prince was spiritually alienated by the complex manouevrings at Elsinore. Now John Caird's National Theatre revival strips the play of politics altogether: the assumption - though this was before the quasi-fascist revolt over petrol prices - is that we live in totally apolitical times and that our only interest lies in the individual sensibility. It's an overtly romantic reading that tells us a lot about Caird and even more about our self-preoccupied age.
Hamlet is a mirror that gives back a picture of ourselves. But what is fascinating about Shakespeare is the way certain plays acquire a renewed vividness at particular moments in time. Peter Brook compares them to planets that either swing closer to the earth in its orbit or drift away. For Brook the bitterness of Timon of Athens brings it into focus, while Othello's jealousy is out of our range: broadly true except that it just takes one exceptional revival - such as Sam Mendes's meticulous Othello - to rescue a play from temporary oblivion.
But the perennial danger with Shakespeare is that the plays get revived more out of civic duty than expressive need: I'd defy any director of the RSC not to admit there are times when they've put on A Midsummer Night's Dream or Romeo and Juliet not because of any commandingly fresh vision, but simply because of the Bardic equivalent of Buggins' Turn. And if critics occasionally sound weary in the face of another return to Athens, Arden or Verona, it is because they can detect the theatrical equivalent of crop rotation.
That is why I bang on about the need to expand the Shakespearean repertory rather than rely on a dozen-or-so box office certs. And I would argue there is a palpable excitement at Stratford this year about the exploration of the Histories. Even the deliberate discontinuity, whereby the plays are staged in widely differing styles on a variety of stages, becomes a comment on contemporary Britain. We live in a fragmented, possibly dissolving kingdom: instead of approaching the plays with the Victorian assurance that they deal with the restoration of order, we find in them an echo of our scepticism about power.
Given a strong directorial intention, I have no problem in staying fresh for Shakespeare: my only difficulty lies with particular spaces such as the Bankside Globe. But different questions arise with post-1880s naturalistic drama where the variations are more closely calibrated. No two King Lears or Tempests ever look or sound alike. But how many ways are there of doing Ghosts or The Cherry Orchard without violating the play? You update Chekhov at your peril: I remember a post- revolutionary Cherry Orchard in which the characters seemed to be survivors of a seismic social eruption which the text itself anticipates.
Chekhov, to come clean, is difficult for the critic. Of course, one loves the plays. Of course, in a great production, one constantly re-discovers them. Peter Stein represented the ravishing beauty of the white-blossomed cherry orchard in a way which made its destruction unbearable. Terry Hands in The Seagull, by placing the interval after the third act, devastatingly showed how Nina and Konstantin are bruised by time while the older characters remain impermeable. What I am dead against, which once led me to demand a three-year moratorium on Chekhov, is the kind of lazy, linen-suited revival which simply swathes the plays in sentimental atmosphere: fortunately there are fewer of those around than there used to be.
I find myself constantly refreshed by what Jonathan Miller calls the "afterlife" of a classic, its possibility of successive re- creation. But the job of a critic would be much easier - and the vitality of the theatre much greater - if we widened the existing repertory. You'd be astonished how many great and not so great plays still go unperformed.
It was a shock this week in Halifax to realise I'd never before seen Euripides' Alcestis on stage: in a sense one still hasn't - since this is a radical Ted Hughes adaptation. The Greeks, the Germans, the French: there are still large tracts of unexplored territory. Even Ibsen we know only in part: I once saw Love's Comedy in rep and The League of Youth at a drama school but I suspect that's it for my lifetime.
Critics themselves are part of the problem: they trot out the old phrase "deservedly neglected" when confronted by anything less than a mainstream classic. Audiences too are wretchedly conservative. But the real problem lies with managements who, with a few notable exceptions, stick with winning formulae with the commercial myopia of a Hollywood mogul.
It has struck me lately, for instance, that we are staggeringly ignorant of British drama from 1900 to 1950. Barrie's Dear Brutus is coming up at Nottingham and Maugham's The Circle at the Oxford Stage Company. But we know next-to-nothing of Pinero, St John Ervine or Monkhouse, not to mention Galsworthy, Bridie or Priestley, aside from An Inspector Calls. If I sometimes get critically testy, it is not with the revival of another Hamlet or The Cherry Orchard, these are great plays one can go on rediscovering all one's life. It is with the debilitating narrowness of the British repertory and with our failure to realise that, outside the accepted masterpieces, lies a wealth of undiscovered plays. Exactly the kind of work we built the National Theatre to explore. But that's another story.
• The Cherry Orchard is at the National Theatre, London SE1 (box office: 0207- 452 3000) till 2001. Michael Billington is the Guardian's chief theatre critic
