Priscilla, Queen of the Desert, Palace Theatre, LondonDimetos, Donmar Warehouse, LondonDido, Queen of Carthage, NT Cottesloe, London

It takes more than classic pop songs and gaudy costumes to make up for a thin script and some tired acting

These songs are the equivalent of silicone implants. The drag-act comedy Priscilla, Queen of the Desert – in this musical adaptation, imported from Australia to the West End – is padded out with a huge synthetic wodge of disco hits, more than 30 cover versions in total. So "Downtown", "What's Love Got to Do with It" and "Girls Just Wanna Have Fun" – as well as, of course, "I Will Survive" – are all crammed in, pumping up the volume and the feelgood factor every three minutes or so, as we schlep with Jason Donovan's Tick and his flouncing fellow transvestites from Sydney through redneck country.

As in the much-hyped 1994 movie, Tick, Bernadette (a veteran transsexual) and Adam (a brattish "gender-illusionist") are journeying across the outback to Alice Springs in a second-hand bus which they call Priscilla. If they arrive before the storyline peters out entirely, they're going to perform their cabaret routines in a casino managed by Tick's accommodating one-time wife, the very existence of whom is a fact he has kept in the closet since joining the fellas-in-frocks brigade.

This show is certainly a gaudy, glitter-strewn spectacular. The bus is like a giant couldn't-be-camper van (designed by Brian Jesus Christ Superstar Thomson). It's fitted out with a cocktail bar, dangling pink plastic flamingos, a giant furry banana, and deckchairs upholstered in rainbow-striped ostrich fluff. The costumes (by Tim Chappel and Lizzy Gardiner) are equally flamboyant. A bunch of divas, including Zoe Birkett from Pop Idol, are flown in on wires like tongue-in-cheek goddesses, sheathed in swans' wings, Meanwhile, the drag queens down below prance around in platform soles, hotpants and rococo wigs stuffed with flowers and fruits.

The problem is that no amount of carnivalesque exuberance can conceal that the dialogue is woefully thin and unfunny. Tick and co's banter and bitching is so parched of wit that I started to see mirages – visions of half-decent jokes shimmering on the horizon – while just about managing to endure the strained double entendres ("Mum always told me to eat my Swedes"), feeble puns ("Shut your von Trapp") and curiously sour, not to say misogynistic snipes ("Don't drop your womb!" for "Keep your hair on!").

It's hard to root for such tiresome travelling companions. To give him his due, Tony Sheldon has droll comic timing as Bernadette, abandoning his demure balletic poise to give a gay-basher a boot where it hurts. The mincing, muscle-bound Oliver Thornton also contrives to make Adam a slightly less ghastly git than in the film. But Donovan is embarrassingly dire, self-consciously and rigidly stumbling through his moves, then turning toe-curlingly sentimental.

Oh, take me back to La Cage aux Folles, over at the Playhouse, and let me once again see Douglas Hodge as the drag artiste Albin. Alas, Hodge has moved on and has donned his director's hat to stage the Donmar's revival of Athol Fugard's Dimetos, a clunking mid-1970s tragedy inspired by a Greek myth.

Jonathan Pryce's tetchy Dimetos is a legendary engineer who has abandoned the city for a backwater. Holed up with his nubile niece, Lydia (Holliday Grainger), Pryce proves to be racked not only by his atrophying commitment to society but also by suppressed incestuous desires – which suddenly explode when a cosmopolitan emissary, Alex Lanipekun's pushy Danilo, makes a move on Lydia.

Pryce copes valiantly with Dimetos' descent into guilt-racked madness. But he's a dry old stick, exuding barely any sexual desire at all. Moreover, Fugard's drama is a rickety structure, with cack-handed revelations, ridiculously rushed catastrophes, its bold prose-poetry tipping over into grandiose philosophising.

In the opening scene, Grainger's Lydia has to drop, scantily clad, down a well shaft to truss a snorting horse (played by a man). By the end, Lanipekun's Danilo is bellowing absurdly elaborate queries at Dimetos: "This rational intelligence of ours, our special human capacity for anticipating, predicting pain – our own or another's – as the consequence of an action was useless, wasn't it?" You can say that again, mate. Hot on the heels of Madame de Sade, this is another unsound choice of script by the Donmar.

Christopher Marlowe's post-Trojan War doomed romance, Dido, Queen of Carthage, also has its longueurs. At first, director James Macdonald fails hopelessly to bring Marlowe's ornate poetry to life. Some of the verse-speaking has so little spring in its step that it slows to a crawl on the Carthaginian shore, where Mark Bonnar's Aeneas and his compatriots are shipwrecked.

Thereafter, however, Bonnar becomes mesmerising in his quietly traumatised account of the Greeks' sacking of Troy. And Anastasia Hille is superb as Dido, surely one of the top performances of the year. She shifts effortlessly from the mini-farce when she is jabbed by Cupid's dart to searing desperation when he abandons her. Hit and miss, but inspired in parts.

'Priscilla' (0844 755 0016) to 26 Sep; 'Dimetos' (0870 060 6624) to 9 May; 'Dido' (020-7452 3000) to 7 May