THEATRE; The Leenane Trilogy Royal Court, London

There's something creepy about the Martin McDonagh phenomenon. If you didn't know that he enjoys a genuine existence as an award-winning 27-year-old dramatist who was reared and still resides in London yet churns out plays set in a half-invented rural Ireland, you'd be tempted to think that he was a clever hoax dreamt up by a committee of postmodernist pranksters. Prolonged exposure to his work - possible now with the Leenane Trilogy - at the Royal Court intensifies this weird feeling of some central absence. Is McDonagh, for all his prodigious gifts for zany "Oirish" pastiche and intertextual Synge-song tricks, several sandwiches short of the full emotional lunch box?

Don't get me wrong. I'm not knocking heartlessness. It's just that, unlike a writer such as Joe Orton, who had the courage of his comic callousness and a ruthlessly logical outsider-vision of the world, McDonagh opts for the less honourable course of giving the heart-strings the odd strum before systematically snapping them. And despite the heavy symbolism of the crucifix that dangles over all three of Gary Hynes's zestfully acted productions, he takes only sniggering pot-shots at Catholic culture, on the level of references to pervy priests and a plot line, in the last play, that has a despairingly ineffective cleric imagine that his suicide may perform the miracle of reconciling two violently feuding brothers. But it all seems very shallow compared, say, with Orton's lethally penetrating take on Christianity ("a bird of prey carrying an olive branch") in Funeral Games.

McDonagh's best work to date remains The Beauty Queen of Leenane, the play that kicks off the trilogy and which won acclaim last year when it was seen solo. In it, a middle-aged spinster (excellent Marie Mullen) eventually kills her possessive canny tyrant of a mother for reasons that are dramatised with a powerful ambiguity. By contrast, in the last play, The Lonesome West (echoes of Sam Shepard), the rancidly volatile central relationship between two brothers is the result of an act of parricide that took place in the past and was a ludicrous case of over-reaction to paternal criticism ("getting your haircut insulted is no just cause to go murdering someone").

This is some indication of the way the plays decline into high-energy, repetitive cartoon: where, in a simultaneous cheeky nod to Playboy of the Western World and to the physical resilience of Tom & Jerry, a gullible youth in A Skull in Connemara can stagger in bloodstained after sustaining dreadful injuries in a drunk driving crash and stick around long enough to save the skin of his would-be murderer, turn the tables on his cop brother who bashes him with a mallet, and engage in conversation about the "puffiness" of going to hospital and about "bumpy rides" at leisure centres, before eventually aiming dizzily for the door. The violence of the plays is self-relishingly out of proportion to its implied sociological causes: the ingrownness of a remote, gossip-greedy community (or lack of community). I found myself fervently hoping that McDonagh did not keep pets as a child.

Hynes's actors all give vivid, strong characterisations - especially Brian F O'Byrne who is in all three plays and offers remarkably varied portraits of gauche decency, hilariously self-important incompetence and demented drippiness. In one play, he has to receive the news of the suicide of the man whose role he performed in the preceding one - indicative of the way McDonagh tries to convince you this is a trilogy by having each new set of characters gossip about people we have already encountered or have yet to meet. But there's no sense of spiritual progression. One isn't asking for the Oresteia, just some position where the alternative to cynicism wasn't sentimentality and which you didn't feel would be undermined yet again if the author had time. Welcome to the world of Martin McDonagh? No, on this showing, you're welcome to the world of Martin McDonagh.

Downstairs at the Duke of York's, St Martin's Lane, London WC2. `The Beauty Queen of Leenane', Fri, Sat mat; `A Skull in Connemara' Wed, Thurs, Sat mat; `The Lonesome West', Sat, Mon, Tues (Booking to 13 Sept: 0171- 565 5000)

Paul Taylor