Waiting for the Barbarians, Barbican, London

Philip Glass's 2005 opera came for its UK concert premiere with a reputation as its composer's strongest recent stage work, and in the knowledge that he had drawn parallels with the war in Iraq. Its source, the novel by JM Coetzee, was first seen as an allegory of the way former South African regimes operated, but the meaning has turned out to be more universal.

A magistrate in a remote border town of an unnamed empire is visited by Colonel Joll, leader of a "special force", spreading rumours that the town will be attacked by "barbarians". Joll requisitions the prison, where he is soon interrogating, torturing and murdering members of these nomadic tribes. The magistrate tries to convince Joll that the tribes seek only their own freedom, a stance that brings suspicion and torture on the magistrate himself. He is released, but with his home commandeered and his loyalty to the empire shattered.

The Erfurt Theatre company brought an assured performance, conducted by the Glass loyalist Dennis Russell Davies. Chorus sang from behind gauze screens. The Barbican ran surtitles, but you could hear nearly every word; evidence first of a superbly judged libretto (by Christopher Hampton), and then of Glass's expertise in word setting.

They made a towering character of the magistrate, forced to find unsuspected doubts and strengths. Richard Salter sang with stamina and exasperated, eventually broken patience. In his complex relationship with one of Joll's victims, an abused girl, he engaged eloquently with Elvira Soukop as her characterisation caught fire. Joll was given an understated menace by Eugene Perry, using the body language of the Bush entourage; Michael Tews gave total conviction to the just-obeying-orders officer who carries out the torture.

Emotional shading and overall proportions caught an understated tone of resignation rather than rage. With Glass, listeners sometimes latch on to the obvious similarity of orchestral figures and harmonies from one piece to another, and miss the uniqueness of colour and pacing. Here, the often light scoring featured quietly growling low brass and wind and some Stravinsky-like inventions for woodwind during the passages that were meant for action without words, which here had to be imagined. No crass onomatopoeia for scenes of torture, just lightly struck percussion and one gradual build-up to a level of intensity that was less about personal pain than a growing shared horror at what was witnessed.