Danton's Death, National Theatre

The longest and most densely historical play by Georg Büchner (1813-37) is a potential monster. In German, Dantons Tod can run to four hours or more. There's little action and much speechifying. In plays by his equally wordy, history-obsessed predecessor, Friedrich von Schiller, there are at least fights, battles, a lot of love - and some sex.

The latter admittedly crashes its way, somewhat psychotically, into Büchner's last and unfinished Woyzeck, one of the strangest yet most influential dramas of the 19th-century European repertoire; and the fairytale comedy Leonce und Lena aside, rarely seen in English, that's it from playwright Büchner, who died of typhoid at 23 - three years younger than our still most lamented Romantic prodigy, John Keats.

Incredibly, the Danton play had to wait another 65 years for its first performance, in Berlin in 1902. Danton's Death, about the French Revolution but also about friendship, loyalty, personal (as opposed to strictly political) courage and betrayal, remains a very big and difficult play to stage in English.

Howard Brenton has taken a step back from it since his first 1982 version. In a new translation for the Olivier, directed by National Theatre debutant Michael Grandage, Brenton has cut all street scenes and sans-culottes - the choric proletarian burbling of the original - and pinned a monster back to a fleet-footed gazelle of a play, now coming in at under two hours. It's become a chamber drama, featuring long-haired Parisian firebrands in tailcoats and breeches who bat back and forth, in relentlessly public-school English, the merits and very considerable downsides of their ghastly 1790s experiment - and which would work well in the National's studio space, the Cottesloe, or on TV or radio.

Epic proportion, embodied by Büchner in a deadly journey Georges Danton took from fiery forger of the Revolution to its most prominent public, and popular, victim, has gone. This is a Danton's Death about precisely that, one man's death surrounded by scoundrels - Robespierre but especially Saint-Just - who bay for it and by condemned allies who part from him affectionately before the guillotine brings it on. (And without giving too much away, the trompe-l'oeil used for four decapitations at the end is really quite ingenious...)

There's virtue in the bare stage - simple tables, chairs and stools are brought on for the big Convention scenes and Danton's "trial"; the only concession to size, so to speak, in Christopher Oram's design are huge, oblong, shuttered, rather sinister windows opening and closing behind a gallery from where declamations are made. The acting is all serviceable, but Toby Stephens as Danton is another weak link in this strangely underwhelming production.

He's natty and articulate, but slight. He seems more to recite Brenton's tumbling and creditably contemporary lines than to be occupying the part. Danton needs heft, a kind of physical heartiness which an almost schoolboyish Stephens lacks. When he takes on his foes, one needs to feel that this man is going to explode, not just expostulate. He's at his best in smaller-scale scenes, like the one in the pre-guillotine cell towards the end where he affectingly comforts his fellow lice-infested prisoners.

By contrast, Elliot Levey is snake-like, thin-voiced and prissily narcissistic as Robespierre - wonderfully underlined on his first appearance as he dons his wig in front of a mirror like a primped courtier of the régime he's so lethally dismantled. You've got a tricky Danton's Death on your hands when you're keener to watch, throughout, Danton's nemesis than the eponymous hero. Alec Newman is also gutsily fanatical as the arguably insane Saint-Just.

I still think this production is in the wrong theatre - in the Cottesloe it would pack a punch; the Olivier demands big thinking and, in this play especially, giant acting. What we get is lucid, watchable but not always terribly exciting: it's Büchner-light. I wonder whether Grandage would do better at Leonce und Lena...

• Danton's Death is in repertoire at the Olivier until 14 October
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