Hairspray, Shaftesbury, LondonYou Can't Take It with You, Southwark Playhouse, LondonCloud Nine, Almeida, London

Tracy Turnblad is the Billy Elliot of Baltimore, 1962. The adolescent heroine of Hairspray is scoffed at for being both white trash and horizontally challenged – a girl of voluminous girth. In this buoyant Broadway family musical, it initially seems she'll never get to dance with the other teenyboppers on Corny Collins' hit TV show.

To realise her dream, Tracy (newcomer Leanne Jones) has to battle with the sneering wicked witch of a producer, Velma (Tracie Bennett), and her slim blond brat who has, hitherto, been the starlet of the show. However, Tracy has go-getting determination; she can boogie and Collins spots her talent. So she does go to the rock'*'roll ball in the end and she wins the heart of her bequiffed Prince Charming. More significantly, she manages to end racial segregation in the process.

The combo of tongue-in-cheek comedy and political protest is remarkably joyous. A flimsy Stars in Her Eyes storyline morphs into a local revolution as Tracy struts her stuff on the dance floor and simultaneously spearheads a resistance movement against the authorities' xenophobic policies. Everybody – black and white – is doing the twist together by the end.

Punters from the Department of Health may throw up their hands at a clinically obese role model who doesn't hate her weight. But Tracy's innate confidence is also a great antidote to the present size zero obsession and the self-scorning craze for putting yourself under the knife.

Directed by the Tony winner Jack O'Brien, this production contrives to be slick but also playful and warm. Brightly coloured, cartoony sets whizz in and out on wheels. The plot is tighter and the script funnier than in the original 1988 film.

Essentially, this is a kind of ebullient panto that has arrived in town a month early and will surely enjoy a long run. Michael Ball is having a blast in the Dame role as Tracy's mum. His salt-of-the-earth Edna is ludicrously charming: a mountain of flesh with twinkling, twirling flamboyance. Even if Mel Smith, as the affectionate Mr Turnblad, is not Ball's match as an actor or singer, they make a delightful odd couple, almost corpsing with laughter in their jokey, smooching duet.

Overall, the orchestra's volume needs turning down, and Jones may not be the world's best dancer but she is nimble on her pins and, along with the rest of the cast, full of beans. Johnnie Fiori is also storming as the lady DJ, Motormouth Maybelle, belting out the rousing anthem "I Know Where I've Been". Bouncy fun.

Another kind of alternative American dream is put forward in You Can't Take It with You. Moss Hart and George S Kaufman's 1937 domestic comedy is rather like an American Hay Fever or a lightweight screwball variation on G B Shaw's Heartbreak House. The Sycamores are a whimsically eccentric bunch. Mr S is down in the cellar making fireworks. His wife, a battily eager playwright, is auditioning a drunk actress. Meanwhile, the couple's ballet-mad daughter Essie is pirouetting around, laying the table and receiving a lesson from her erratic, histrionic Russian-refugee dance master, Boris Kolenkhov. Then in a farcical confusion of dates, the wealthy fiancé of the Sycamores' other daughter, Alice, turns up for dinner in the midst of this chaos with his stiff, bug-eyed parents in tow.

The snag is that some members of director Gavin McAlinden's large fringe ensemble can't act to save their lives. Alice Sycamore looks as if she's wooden to the core. Southwark Playhouse also needs to rake its view-blocking untiered seats if punters aren't to feel like flies on the wrong side of the wall.

Still, this new auditorium, under the arches by London Bridge, is a fine spacious venue with real promise. The dialogue is quirkily hilarious and Gawn Grainger proves delightful as Alice's mellow grandfather who resists the taxman and, thought-provokingly, advocates dropping out of the rat race because life is too short.

All the same, this pales by comparison with the pitting of Marxist ideals against ambitious capitalism in Awake and Sing!, Clifford Odets' 1935 Bronx family drama superbly revived by the Almeida early this autumn. Cloud Nine now takes its place. Thea Sharrock's revival doesn't quite make Caryl Churchill's 1970s experimental piece about Victorian values look like a categorically great modern classic. In the first half, the 19th-century colonial household, ruled by the superficially pukka patriarch Clive, is peopled by 2-D stereotypes. Behind the façade of respectability, almost everyone is lusting and sexually digressive (adulterous, lesbian, homosexual and paedophile) – so that it almost feels schematic.

In the second half, it hardly seems startling (from today's perspective, at least) that a gathering of 1970s characters in a park is more liberated, though still not entirely happy.

That said, Sharrock's cast is highly amusing as the starched Victorians, rattling off lines in brittle accents – not least James Fleet's Clive with his preposterously bombastic surges in volume. Nicola Walker is also poignantly febrile as the effeminate little boy Edward and, later, the uptight grandmother Betty.

The use of counter-casting (women playing men, white playing black, etc) also complicates matters. It keeps you mulling over the kaleidoscopic shake-up of the actors and their allotted roles long after you have left the theatre.

'Hairspray' (0870 040 0046) to 15 March; 'You Can't Take It with You' (0870 060 1761) to 17 Nov; 'Cloud Nine' (020 7359 4404) to 8 Dec