"WORDS, WORDS," says Guildenstern. "They're all we've got to go on."

Well, perhaps not all; but it is true that in Rosencrantz and Guildenstern Are Dead, as in most Stoppard plays, it's words and ideas that are the engine of the drama, and what's happening on stage can often seem like a footnote to the real action contained in the language. Because of this concentration on the spoken, it's fashionable to decry Stoppard as essentially a radio playwright, someone with no real sense of how theatre works. Certainly, it's striking how well a play like Arcadia survived the transition from stage to radio a couple of years back, and how badly In the Native State survived the transition from radio to stage in the shape of Indian Ink.

But Stoppard can work superbly on stage, if you're prepared to go with the flow and let the words do the, er, talking. Sadly, watching Matthew Francis's revival of Rosencrantz and Guildenstern, which opened on Thursday at the National, you get the impression that he has taken too much to heart the notion that Stoppard doesn't really write for the stage, and he's tried to make up for it with an ostentatiously theatrical production (big costumes, moving sets, hammy acting) that swamps the play's speculative wit. There are too many moments - the entry of the company of Tragedians, on their way to Elsinore, the sea-fight with pirates and almost all the bits of Hamlet that survive in Stoppard's play - where there's a loudness and vulgarity about the staging (especially about Lez Brotherston's unattractive design) that seems out of keeping with the essential intimacy of the piece.

The redeeming feature is Adrian Scarborough and Simon Russell Beale's edgily charming double-act as the two attendant lords. They manage the swift-moving cross-talk sequences very well ("Shouldn't we be doing something constructive?" "What did you have in mind? A short, blunt human pyramid?"); but then, those are a gift to actors. What's more impressive is the way they manage to convey, beneath the humour, the shifts in the balance of power between the easy-going, unquestioning Ros and the nervy, thoughtful Guil. They bring over the insecurity of characters who aren't even sure they exist outside somebody else's imagination. If the rest of the production had some of the sharpness and reticence of the scenes when they are alone together on stage, it would be theatre of the best kind.

There's an imbalance of words and action, too, in John Barton's staging of Cain for the RSC at the Pit. Here, it's the words that dominate. Byron's poem wasn't written for performance, and it's hard to see how you could turn it into something genuinely dramatic without distorting its philosophical purposes.

It's certainly a fascinating work, set in a cleverly imagined post-Eden world, where angels with fiery swords are part of the everyday landscape and where Adam and Eve and their children consort regularly with spirits. In this world, though, where God is a near neighbour and his words are treated with a very literal reverence, Cain is a misfit. He has too restless a mind ever to be as unquestioningly grateful and obedient as his sister- wife Adah, or his father Adam (whose motto is: "The mind which questions mars the thing it questions and mars itself").

The poem's full title is "Cain: A Mystery" - according to Byron, "in conformity with the ancient title annexed to dramas upon similar subjects, which were styled 'Mysteries or Moralities'." But the implication is inescapable that Cain is himself a mystery; the subject of the piece is his need to understand who he is. God won't give him answers; so Lucifer offers them instead, taking Cain on a trip across the universe to show him how insignificant man is in the scheme of things, and debating with him about the problem of pain, necessity and free will, and other fundamental theological issues.

The whirl of ideas, and the language in which they're expressed, are often striking; but while the action wheels across the universe, the drama remains earthbound. You can admire Barton's resolutely minimal staging, but it's very hard to enjoy it. It doesn't help that so much weight is thrown on to Marcus D'Amico, who as Cain is on stage for nearly two hours without a break; you can see the cogs whirring too much in his performance. There are compensations in Thusitha Jayasundera's intelligent, anguished Adah - and in John Carlisle's marvellous Lucifer, with his sad, mocking eyes. At the end, after he's killed Abel, Cain is exiled to the land of Nod; and to be honest, I felt I was heading in that direction myself.

You can't complain about a lack of dramatic action in Dumas' swashbuckler The Tower, now exhumed at the Almeida. On the other hand, you can complain about a lack of coherence, a wild uncertainty of tone and some highly peculiar language. The play marries elements of the Oedipus and Bluebeard myths, placing them within a conglomeration of melodramatic conventions that zigzag between high passion and the grotesque. It's set in 14th- century Paris, where every morning the bodies of young, high-born men are being fished out of the Seine with their throats cut. It turns out that they've been taken to the royal stronghold Tour de Nesle, where Marguerite of Bourgogne, Queen of France (Sinead Cusack, giving a very creditable impersonation of the wicked queen from Snow White), gives them a thorough pleasuring and then disposes of the evidence.

English literature doesn't really have any equivalent for the weird melange of chivalrous convention and morbid, transgressive sexuality that's at the heart of this play - in which Marguerite doesn't seem to be aware of any contradiction between her vicious sexual appetites and the pure courtly love she shares with the captain of her guard, young Philippe Gaultier. By night, in the tower, she's by all accounts given to uttering disgusting words, oblivious to propriety and decency; by day, she's on a strict "no tongues" regime.

It would be easy to play this as pure, camped-up comedy; Howard Davies tries something more difficult, allowing you to see the humour, but also trying to get across the darker themes of cynicism and misogyny underpinning the drama. He's greatly assisted by Charles Wood's boldly idiosyncratic translation, which slips in and out of stage French ("Ca ira! It goes on") and jarring literalisms ("You are congratulate").

The project doesn't work - the switches of tone are too confusing, not just for the audience, but for the actors. Only Adrian Dunbar seems to have gauged correctly how seriously it should all be taken: he's terrific as Buridan, a hard-bitten soldier of fortune who escapes from the Tower and determines to turn the experience to his own advantage, bringing exactly the right qualities of toughness, disillusion and mystery to the part.

Which doesn't leave much room to talk about Company (see also Michael White, page 15), Sondheim's merciless anthology of modern marriages, at the Donmar. Then again, we can do this one fairly swiftly: Sam Mendes's staging is altogether superb, featuring a batch of excellent supporting performances (special mention to a jittery, brilliant Sophie Thompson), and a stunning central performance from Adrian Lester as Robert, the unmarried male around whom everybody else's action revolves. I wouldn't say you should kill for a ticket; but you could probably justify some minor maiming.

'Rosencrantz and Guildenstern Are Dead': Lyttelton, SE1 (0171 928 2252). 'Cain': The Pit, EC2 (0171 638 8891). 'The Tower': Almeida, N1 (0171 359 4404). 'Company': Donmar, WC2 (0171 369 1732).