IoS theatre review: Privates on Parade, Noel Coward Theatre, London Viva Forever! Piccadilly Theatre, London In the Republic of Happiness, Royal Court, London

Simon Russell Beale's Terri is as camp as a row of tents in Privates on Parade, Peter Nichols's 1977 seriocomedy about a British Army song and dance unit in Singapore and Malaysia, entertaining the troops in 1948.

The production launches the Michael Grandage Company on its star-studded residency in the West End. And Beale instantly steals the limelight as Terri, the unit's drag queen – built like a tank and decked out in super-flamboyant frocks for his musical numbers. Clumping around in a Carmen Miranda outfit, Beale puts most pantomime dames in the shade, with a mass of flounces sprouting from his barrel chest and fruit stockpiled on his head. He is up to his ears in double entendres too, cocking an eyebrow with priceless comic timing.

In this rite-of-passage drama, Private Flowers (Joseph Timms) is the straight, initially homophobic innocent who learns that the military includes gays with hearts of gold. Nevertheless, the unit has to contend with a bigoted sergeant (Mark Lewis Jones) and a gung-ho, superciliously racist commander (Angus Wright) who instructs Flowers to ditch his mixed-race sweetheart, Sylvia (Sophiya Haque).

The let-down, if you're expecting uniformly top-notch acting, is that the younger cast members don't pass muster, and the storylines are sketchy. That said, Nichols is experimenting with the borderline between a play and a revue. Banter in the dressing rooms flows seamlessly into the unit's show-time routines.

Beale's image will be burnt on the mind's eye for a long time to come, I suspect, as he poses in a blonde wig under a golden spotlight, head thown back in a Kenneth Willliams-like rictus . When given the chance, he also plumbs depths of acute loneliness and simmering indignation. Still, his performance on press night looked fractionally anxious. Was he under the weather or worried about the synchronised dance moves? Meanwhile the usually excellent Wright seemed uncertain if his pontificating character should lecture the onstage chaps or us in the auditorium. Perhaps best give Grandage's cast another week to warm up.

Don't race to catch the new musical Viva Forever! If the title is anything to go by, it's destined to run and run. Or is this tawdry stage show about a tawdry TV series – with ill-fitting Spice Girls songs – a vision of dumbed-down British culture feeding on itself with an inane, vampiric grin?

In case you've not been bored to death already by endless talent shows on the box, Jennifer Saunders has here churned out a jawdroppingly witless script for producer Judy Craymer (previously of Mamma Mia!) wherein wannabe girl-band members are selected for a televised competition called Starmaker.

The foursome swear eternal friendship only to bust up when a mean-as-hell panel judge, Sally Dexter's Simone, prowling around like Cruella de Vil, picks only one of them for the final round. Though supposedly a grrrrl with a mind of her own, Hannah John-Kamen's Viva lets herself be isolated without phone contact, put on a needless diet, made-over to others' tastes, then dragged into a sensationalist set-up, to meet her birth mother as the cameras roll.

John-Kamen's performance is nicely grounded. So is Sally Ann Triplett's as her hippyish adoptive mum, but she and Viva's buddies – while supposedly gatecrashing Starmaker – are surely playing right into its hands. Indeed, I kept hoping there would be some dark, final twist, in which, like The Truman Show, it turned out everyone had cynically signed up to Simone's faux world.

At the curtain call, where the actual Spice Girls were bundled up from stalls to stage, Victoria Beckham looked miserably embarrassed while the rest obligingly whooped.

Finally, in the avant-gardist Martin Crimp's satirical, absurdist and strangely gripping new play In The Republic of Happiness, a suburban family sit stiffly over Christmas dinner, with polite small talk veering off into senile fantasies and vitriolic rants. Like some kind of visitation, Paul Ready's possibly predatory Uncle Bob materialises out of nowhere in a silver Puffa jacket, bearing tidings of how his partner, Madeleine, would like to wipe them off the face of the earth.

Michelle Terry's Madeleine then appears, with a silky smile, saying she and Bob's new life, far away, is going to be thin and clean, like a pane of glass. Next thing you know, the cast have turned into some kind of middle-class cult, smiling at us and spouting – as if reiterating rote – about how individualistic they are; how none of their life choices are political; and how they're on the path through personal trauma, to happy, gym-fit immortality.

Dominic Cooke's excellent cast, including Emma Fielding and Stuart McQuarrie, are teasing and riveting. A few sequences are prolix and the interspersed rock songs lack bite, but Crimp's unhinged structures are potently dreamlike, startlingly comical, and disturbing.

'Privates on Parade' (0844 482 5141) to 2 Mar; 'Viva Forever!' (0844 871 3055) booking to 1 Jun; 'In the Republic of Happiness' (020-7565 5000) to 19 Jan

Merrily We Roll Along , Sondheim's regret-tinged comic musical about stardom and wrecked friendships, is superbly directed by Maria Friedman at the Menier, London (to 9 Mar). Or catch Going Dark at the Young Vic (to 22 Dec), an immersive, poignant weave of luminous lectures on the universe and the tragedy of an astrophysicist going blind.