Realism, Royal Lyceum, Edinburgh<br/>Particularly In The Heartland, Traverse, Edinburgh<br/>Troilus and Cressida, King's, Edinburgh<br/>Sugar Mummies, Royal Court Downstairs, London

Just last week I was applauding the new National Theatre of Scotland company for taking the Edinburgh Fringe by storm with Black Watch, their docudrama about the regiment in Iraq. Well, now the NTS has kicked off the International Festival exhilaratingly too. Written and directed by Anthony Neilson, Realism is a boundary-pushing and teasing portrait of the artist, of everyday life and unhinged fantasies. You might, in fact, say Realism is Neilson's answer to Virginia Woolf's stream of consciousness, experimentally exploring how mundane actualities mesh with our wandering thoughts - only it's more like Woolf crossed with a dreamlike version of Men Behaving Badly.

A bed, a sofa, a fridge, washing machine and toilet are strangely scattered across a slope of white sand. Downstage, a bloke called Stuart McQuarrie (played by Stuart McQuarrie) is moping and slobbing around in his boxer shorts. Fat, pale, munching on cereal, scraping cat food off his foot, he's feeling like a loser. He has recently ditched a girlfriend and is perhaps going quietly mad on his own, occasionally visited by his laddy mates (or imaginary friends?), by his former lovers and memories of his mother and father (the latter gamely played by the playwright's own actor-dad, Sandy Neilson).

One moment, Stuart's four-letter expletives about his gas bill can turn into a surreal cabaret number. The next, his mother's remonstrating voice is issuing from the washing machine, muffled by his dirty laundry. At one point, he sits thinking seriously and mournfully on the loo, whilst wiping his posterior, and in another scene his ex takes a pee, which turns into shameless lesbian-spanking fantasy. It must be said, some of the vignettes do verge on the tiresomely puerile and Edinburgh's most conservative theatregoers clearly didn't care for Neilson's taboo-breaking. But the mood swings are often truly startling, with moments of profound sorrow alongside wild silliness.

The theatrical inventiveness is inspired. Realism also makes a serious point about unromantic realities; and the borderline between present adulthood, the past and persistent childishness is deliberately blurred.

At the Traverse as part of the fringe, the Team is another exciting avant-garde troupe from New York (Team being short for "Theatre of the Emerging American Moment"). Admittedly, what they are trying to say about US society remains nebulous in their devised piece, Particularly In The Heartland. Three naïve Kansas siblings, whose parents have apparently been swept away in a tornado, establish a cranky but perhaps ultimately more loving society on their isolated farm. They take in a weird clutch of strangers including a traumatized bisexual businesswoman who has dropped from the sky and the ghost of Bobby Kennedy. What is really exciting is this company's adventurous, highly idiosyncratic aesthetic - combining a junk shop of props with comic charm, fierce physical charisma, sharp acting, batty musical interludes and deeply bizarre images - most memorably a blood-soaked girl in a wheelbarrow laying an egg from her mouth. If the Team stick together and continue to mature, they could go far.

Meanwhile, back at the International Festival, the veteran German director Peter Stein presents a creaky production of Shakespeare's Troilus and Cressida with an underpowered British cast. On opening night, the squeaking hydraulics of the set's huge, ugly, tilting metal wall literally ground to a halt half-way through, so we all had to troop back the next afternoon: an epic bore. All right, Stein does attempt to convey the time-corroded shabbiness of Shakespeare's cynical vision of the Trojan war with the Greek generals looking like a bunch of ageing tramps - all pallid paunches and ragged overcoats. However, the muscle-bound and bronzed Trojans surely look unintentionally silly, striding around in leatherette underpants and lashings of fake tanning lotion, as if auditioning en masse for The Rocky Horror Show.

Most of the company deliver their lines terribly slowly, and too much of the acting is B-rate. Only David Yelland's surreptiously sardonic Ulysses has any real bite. As for the tarnished titular romance, Paul Jesson's sleazy Pandarus can be painfully intrusive but Henry Pettigrew's Troilus is a wearisome whinger and Annabel Scholey's fickle Cressida strains whenever she tries to shift up a gear into agonised grief. Stein adds a mute scene too, endowing both lovers with a tragic ending where Shakespeare is more radically bleak, just leaving them to vanish into the maw of time.

Finally, the Royal Court offers a feeble new play by Tanika Gupta about sex tourists in Jamaica, whither UK and US ladies apparently flock and pay hard cash to the local hunks who live by male prostitution. Staged by Indhu Rubasingham on a circle of sand with projected palm trees overhead, Sugar Mummies never has the ring of closely-observed truth about it. Many of the characters feel like crude caricatures, from the farcically swaggering studs to the lusting white women who, when disappointed, instantly prove to be seething vicious racists. The drama lurches clumsily into melodrama and sentimentality. Well below par.

k.bassett@independent.co.uk

'Particularly In The Heartland' (0131 228 1404), to 27 August; 'Troilus and Cressida' (0131 473 2000) to 26 August; 'Sugar Mummies' (020 7565 5000) to 2 September