The biggest event of the Royal Opera’s 2011-12 season, Berlioz’s five-act epic The Trojans turns out to be a game of two halves in recently knighted Sir David McVicar’s new production. The first part of the evening, dealing with the fall of Troy, is thrilling music theatre. In the second part, however, when we move on to the section dealing with the Trojans in Carthage, the show loses distinction and coherence.

A scene from Les Troyens at the Royal Opera House, London Photo: Tristram Kenton

There’s much to admire up to the first interval. Es Devlin’s mighty set offers a gigantic metallic city wall and a monumental Trojan horse, made up of discarded weaponry. Visual references are made, especially in Moritz Junge’s handsome costumes, to the period of the Second French Empire, whose hubris and folly led up to the defeat and destruction of the Franco-Prussian War of 1870 and the Paris Commune of 1871. (Berlioz had composed his largest work - which was never performed complete during his lifetime - between 1856 and 1858.) Anna Caterina Antonacci bestrides the stage with superb engagement as Cassandra, doomed to foretell the downfall of her city but unable to convince its citizens of imminent danger; her passionate singing and acting provide the evening’s finest single performance, but both staging and music-making reach considerable general heights as disaster overtakes Troy.

Later on the design falters. The North African milieu is suggested in bright costumes and with a vast, layered cityscape of warm Mediterranean colour, but that’s more or less it for the last three acts. When a drop curtain comes down for Dido’s grand scene of farewell, it looks odd; one expects it to rise to reveal something eminently striking for the final tableau. Instead, Dido’s funeral pyre is meagre and there’s a curious reappearance of the Trojan Horse in altered, semi-human form. Quite what this is intended to convey is uncertain.

Other mistakes are made. A lengthy ballet sequence in Act IV is dully choreographed by Andrew George, and could be dropped altogether. The more important Royal Hunt and Storm is surprisingly poorly staged. Visual momentum and stagecraft both lose impetus.

Individual performances provide a partial salvation, though Royal Opera regular Eva-Maria Westbroek scarcely seizes on the regal potential of Dido, ably supported though she is by Hanna Hipp as her sister Anna and by Brindley Sherratt as her chief minister, Narbal.

To the American Bryan Hymel falls the unenviable task of replacing everyone’s favourite tenor, Jonas Kaufmann, the originally announced Aeneas. He acquits himself more than creditably, his tone bold and free, his high notes nicely placed and his manner sufficiently heroic to convince.

Antonio Pappano conducts a secure performance, but even here some electricity is missing. Berlioz’s style is difficult to master, and despite some impressive work from orchestra and chorus the essential spirit of this grandiose masterpiece proves elusive.