Any sex play by David Mamet comes with “controversial” padlocked to it: the teasing ambivalence of Oleanna in 1992 ensured that. But his post-Weinstein drama is not provocative: it’s just a feeble fizzle.

Bitter Wheat fails on every front. It is advertised as farce but, as directed by Mamet himself, is too flaccid to raise more than a couple of laughs. The Hollywood mogul who tries to bamboozle a young actress into bed with the promise of stardom is so self-evidently a creep (“You’re a Korean and you can’t give me a massage”) that it’s hard to believe he ever took anyone in. John Malkovich paws, roars and unzippers his way around the stage: he is a grisly force, but he is not written as a human being; he might have escaped from Where the Wild Things Are. By making him merely a monster the play lets itself lazily off the hook of real controversy: the systematic and systemic abuse of power.

Plenty else is wrong. The plot takes a bonkers sudden leap in the second half. The satire on the film industry, which Mamet took to pieces scathingly in Speed-the-Plow, is desultory: all juries are rigged; all critics bought off. This is not only a waste of Malkovich’s talent but of Ioanna Kimbook, impressively poised in the limply written part of the young actress. And of Doon Mackichan, coolly persuasive as his inscrutable – on message or offside? – assistant, ticking around like a deathwatch beetle. An evening is too precious to give up to watching this. Not so much wheat as chaff.

What a relief to turn to the rich rest of the week. Now at last we know what Samuel Taylor Coleridge was really on about in Kubla Khan. His stately pleasure dome is perfectly evoked by Giffords’ little top: in it, audiences feast on honey dew and drink the milk of paradise.

Far removed from the fluorescent contortions of Cirque du Soleil, Giffords mingles sweetness, skill and spangle. Crucially, director Cal McCrystal weaves what could be merely a string of acts into a free-flowing story. In Xanadu he has found the perfect vessel. Coleridge’s mazy motion poem provides a title and 1970s psychedelia supplies mood and music. The experience is complete. The sweet tent serves sherbet fountains. Performers have headbands, granny specs, flowers in their abundant hair, flared jeans in two-tone denim. The interval is announced by performers pointing: “Way out, man!”

The action is joyfully twirled around by Michael Fletcher – holding the Liverpudlian line with saucy tunefulness, so that one moment of wonder – comic or hair-raising – rolls into another as in a pot-induced dream. Doves flutter from – where? – to land on shoulders; bodies balance on galloping horses or fly through the air on a trapeze, as if wishes had wings. There is a familiar loved star in Tweedy the actually funny clown, who arrives tugging his pet – an iron called Keith – on a lead: “Sit! Stay!” Lil Rice is a newer glory: unyielding, glittering, with a voice that shimmies through sandpaper, as she spins round the ring spread-eagled in her cyr wheel. And Nell Gifford, queen of the circus, appears on horseback through white clouds of mist to the sound of the Kinks’ refrain… thank you for the days.

There are hardly any thanks, and not much hope, in Strange Fruit. The energy in Caryl Phillips’s 1981 play comes from elsewhere. This was Phillips’s first play: it is sometimes over-explanatory and is given too leisurely a production by Nancy Medina. But its angers and bewilderments still burn strongly. It’s a fitting last production for Madani Younis’s artistic directorship, opening on the day Lynette Linton announced a bright array of new work and revivals.

The title only partly misleads. The action is not based on the lynching song made famous by Billie Holiday: it’s based in Britain – and on the systematic lynching of people’s aspirations. There is a relay race of bullying here. Rakie Ayola’s Vivien – delicate, cautious, withheld – came to London from Jamaica, leaving a drunk husband behind her. A busload of factory workers sing Bye Bye Blackbird at her; she is spat at and punched.

It seems to her sons that her wish for English acceptance pushes them into a straitjacket of gentility: her vision of white middle-class life spills out of the auditorium in Max Johns’s design: a china alsatian dog sits near the threshold. One son is more angry than any stage character since Jimmy Porter: Jonathan Ajayi is terrific as a morphing fury and a strutting rebel. He takes his revenge in brutal insults to his white girlfriend. Tilly “just because I’m not coloured doesn’t mean I’m stupid” Steele is extraordinary, congealed with the fear of being rejected.

It is startling how much of a feminist play this is. Yet for those of us whose families have never been transplanted the challenge it poses is different. The older son sees his brother playing black and his mother playing white. How do you know when you are playing yourself?

Star ratings (out of five)
Bitter Wheat ★
Xanadu ★★★★★
Strange Fruit ★★★★

• Bitter Wheat is at the Garrick, London, until 21 September

• Giffords’ Xanadu tours until 29 September

• Strange Fruit is at the Bush theatre, London, until 27 July