A Doll's House, Donmar, London<br>The Observer, NT Cottesloe, London<br>Grasses of a Thousand Colours, Royal Court Upstairs, London

The Donmar's new Ibsen isn't so much a clever interpretation as a bit of questionable rewriting

The wife of a cabinet minister involved in fraud? Surely not! Written by Ibsen in 1879, A Doll's House is renowned for having been startlingly ahead of its time in terms of feminism. But who'd have thought it would be so up to the minute, financially, in May 2009?

Zinnie Harris's new English adaptation is not in modern dress. With the setting shifted only to London in 1909, Gillian Anderson's Nora is robed in belle époque gowns, and her ministerial spouse, Thomas (Toby Stephens), wears wing collars to work. Nonetheless, the scandal they face is uncannily topical, chiming with this month's "Moatgate" furore over parliamentarians' use of the kitty.

Anderson's Nora has been fiddling the household expenses and has risked fraud to supplement her husband's income. The couple have just moved into a new mansion – still strewn with unpacked tea crates – when she finds herself threatened with an exposé.

Stephens's Thomas dreads the consequences of tarnished Westminster reputations. "As politicians, our staple is trust," he underlines. The audience hoots. This could have been written yesterday!

Erm, actually, it pretty much was. That line isn't in Ibsen's original script. Torvald (the Thomas of 1879) wasn't even a politician. He was a small-town lawyer turned bank manager. One might complain that Joe Public is being deceived by "new versions" such as Harris's. More transparency is needed: programme notes about such adjustments, at least.

It was primarily the sexual politics of A Doll's House that scandalised Victorian theatre-goers, and that issue plays second fiddle here. It emerges strongly only at the close, when Nora walks out on her patriarchal husband. Stephens is left crumpled on the floor, crying like a baby. Prior to that, he is very amusing as the swanky politico. He and Anderson also make their domestic relationship instantly recognisable – not dated – with frisky, teasing amorousness. Disappointingly though, Anderson is never quite convincing when wringing her hands about Christopher Eccleston's Kelman, the blackmailing desperado.

Tara Fitzgerald is hit and miss too, playing Nora's impoverished friend Christine as a testy socialist. Maybe the blame lies with director Kfir Yefet. Overall, the acting feels jerky, not fully joined up, regardless of star casting.

In Matt Charman's outstanding new play, The Observer, the British government is keeping Anna Chancellor's Fiona under surveillance. She is essentially running the international observation team in an unnamed ex-colony in Africa. Their mission is to assess – supposedly objectively – how free and fair its first democratic elections are.

With discussions about voter registration and electoral committees, this could be theatrically arid, yet Richard Eyre's superb ensemble of actors is gripping. They subtly depict a world where diplomacy and bureaucratic pragmatism are eroded by improprieties and smouldering tensions. Charman also sharply questions the possibility of true impartiality. This young dramatist has progressed by leaps and bounds since his 2007 NT debut.

The set changes are slightly distracting, being visible in the background of other scenes through chinks in a wall of drop-down blinds. Perhaps such snooping is being invited, though. In The Observer, after all, everyone is monitoring everyone else. James Fleet is charmingly droll then chilling as the Foreign Office's smiling, spying civil servant. Chuk Iwuji shines as Fiona's smitten but wary translator. Cyril Nri doubles as a delightfully sunny barman and icy army general. Meanwhile, Chancellor's Fiona gradually loses her cool under stress. As her long-distance marriage disintegrates, she lets her political sympathies and passion destroy her professionalism. Highly recommended.

In Grasses of a Thousand Colours, some kind of nightmarish apocalypse is engulfing the world. A scientist has made animals and people turn omnivorous, and now they're malfunctioning, crazed and terminally sick. This is the world premiere of a stupendously wacky, blackly comic chamber piece by the Hollywood actor and experimental playwright Wallace Shawn.

He himself plays the scientist, rolling up on stage in a black silk dressing gown, looking like a bonkers gnome crossed with Noël Coward. He waves hello to the audience and says he's appreciating each of us like a box of chocolates, and some of us are whisky flavoured. Then he pulls out a fat book and launches into his memoirs, soon digressing preposterously, in graphic detail, about his penis and his erotic adventures with women and fairytale cats in palaces.

I have to say this made me laugh a lot, even if length does matter and Shawn bangs on for over three hours. He is unedited by his director, André Gregory, and his darkening ending lacks real weight.

Nevertheless, the way his storytelling slides between the everyday and dreams is strangely brilliant, liberated and sharply focused. His materialising fantasies are wonderfully tongue in cheek too. The voluptuous Jennifer Tilly pops out of nowhere, tipping the audience the wink. And a prowling Miranda Richardson rolls over the back of Shawn's sofa with glitter-dusted skin and feline makeup. By the end, she looks like something from Cats staged in an asylum.

'A Doll's House' (0870 060 6624) to 18 July; 'The Observer' (020-7452 3000) to 8 July; 'Grasses of a Thousand Colours' (020-7565 5000) to 27 June