Really Old, Like Forty Five, NT Cottesloe, LondonA Raisin in the Sun, Royal Exchange, ManchesterMy Stories, Your Emails, Barbican Pit, London

Tamsin Oglesby's tragi-comedy about dementia is certainly topical but has little else going for it

Its title sounds like a phrase from a tactless teenager in a family sitcom. But in its concern for Britain's rising tide of dementia, unsatisfactory state care for the elderly and the arguments for euthanasia, Tamsin Oglesby's tragicomedy, Really Old, Like Forty Five, could hardly be more topical.

Certainly, the recent news that a healthy diet might stave off Alzheimer's chimes startlingly with heated negotiations in the office of Paul Ritter's weaselly health minister Monroe – though he scoffs: "Are you seriously suggesting we forget the drugs and give everyone mung beans instead?"

Sir Terry Pratchett's much lauded lecture in favour of assisted suicide, broadcast on Monday, also finds echoes in the play's more sardonic slant. The trials of a memory-regenerating drug that Monroe has been promoting produce various problematic side-effects, not least death. So his clinical advisers – without batting an ethical eyelid – remarket the concoction as euthanasia pills. Hey, overcrowded wards will no longer be a problem.

Unfortunately, other than its topicality Anna Mackmin's production has dismally little to recommend it. The play's vision of a nanny state – though part-futuristic – involves oldsters being obliged to sign up as adoptive grandparents and serve as medical guinea pigs to earn government-dispensed points. Yet it is Oglesby's script itself that needs more careful nursing, if not a complete overhaul.

The storyline attempts to follow an extended family through Monroe's impersonal system as Judy Parfitt's intellectual Lyn succumbs to dementia. But their journey is garbled, unengagingly bitty and inconsistent in tone. The satire often falls flat, and pathos flickers belatedly only when Lyn's hands-off daughter (Amelia Bullmore) explodes with exasperation and forces her mother to acknowledge distressing skeletons in cupboards. That rings true. However, most of the time Mackmin's cast members seem to have been left to their own devices, hurrying through speeches tacked together with all the skill of Dr Frankenstein's neck surgery.

Maybe Parfitt was suffering from press-night nerves, but her wooden delivery was, at points, an unwitting match for the surreal android-nurse, Michela Meazza's Mimi, who regurgitates tinny, faux-empathetic phrases and makes noises like a purring cat crossed with a clanking steam train. Meazza's robotic moves – plumping pillows like a stab in the back – supply the show's only truly funny moments. But Gawn Grainger's sci-fi horror shtick, as Lyn's wrinkle-phobic brother, wouldn't pass muster even as am-dram, as he scrabbles with a rubber mask that's meant to be a disintegrating face-lift. Really bad, like one out of five.

Closely observed family tensions and far-reaching social issues are much more grippingly yoked in A Raisin in the Sun. The Younger family – stuck in a cramped tenement in Chicago's ghettoised South Side – has an irrepressible capacity for dreaming of a better life in Lorraine Hansberry's heart-rending modern classic about being black in the 1950s. Beneatha Younger is a bright college girl who is determined to become a doctor. Her brother Walter is concocting a lucrative scheme to start up in business with two of his pals. His wife, Ruth, yearns – along with his elderly mother, Lena – for the day when they'll be able to buy a sunlit home of their own in a better neighbourhood.

In Michael Buffong's exhilarating regional revival, the old linoleum floor in the Youngers' kitchen is flecked sky blue like an expression of their aspirations, under the shadow of a rusting fire escape. The whole family is just waiting for a windfall – an insurance pay-out – and then they'll be on their way. But that's not counting on the stack of prejudicial glass ceilings that are going to hold them down, including not only pernicious white racism but also their own internecine conflicts.

Buffong's ensemble shift superbly from quiet tetchiness to seductive ardour, from jubilant partying to fierce, howling grief. Ray Fearon, as Walter, captures burning despair under cover of feverish drunken laughter. Jenny Jules has a beautiful, bruised tenderness as Ruth. Tracy Ifeachor could tone down the scampering, but her adolescent élan is spot-on, and Starletta DuPois's matriarch has wonderful gravitas and warmth. Great stuff.

Maybe Walter will never make it as an entrepreneur, but Ursula Martinez has all the appearance of a City exec introducing her latest presentation at the Pit: My Stories, Your Emails. In trim grey suit, tight chignon, lipstick smile, mile-high stilettos, she is power-dressed, prim, posh, provocative.

In fact, this is her trademark outfit as a performance artist who deals in the teasingly outré. At the centre of her experimental comedy show is a video of Martinez performing her burlesque strip routine, Hanky Panky, thrusting her pelvis with a gusto which is delightfully ridiculous.

This is preceded by a string of quirky autobiographical anecdotes: deadpan one-liners like fragments of memory about her Spanish-British roots and Lancaster Uni days. It's then followed by a bunch of appallingly funny, pitiful emails – plus excruciating personal photos – sent to Martinez by cranks and weirdos who've seen Hanky Panky posted (apparently without Martinez's consent) on the web. What's curiously charming is the ludicrous naivety of these guys (assuming they're for real) and the gentle wit of Martinez's exposé of them.

'Really Old, Like Forty Five' (020-7452 3000) to 17 Mar; 'A Raisin in the Sun' (0161-833 9833) to 20 Feb; 'My Stories, Your Emails' (0845 120 7750) to 13 Feb

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