An opera company able to extricate itself from an eleventh-hour fix as WNO did before the premiere of its new production of Schoenberg's Moses and Aaron is likely to deliver on other fronts.

Hours before the curtain rose on this uncompleted 20th-century work, understudy tenor Mark Le Brocq stepped forward to deputise for the indisposed Rainer Trost as Aaron. Job done. It did, however, require company boss and artistic director David Pountney to appear stage left and make an announcement.

The work is not only unfinished - two acts instead of the projected three - it's also Schoenberg at his most uncompromisingly atonal. It's also not a theatrical masterpiece, at least not in the versions able to be undertaken by modern opera companies. The drama is as much in the music as on stage among the unsettled Israelites, in this case an augmented WNO chorus with embedded characters, and their relationship to the eponymous brothers.

The opera is very much a chorus-led event, despite the differences between the brothers and the way their views of an ineffable God affect their ability to lead by example. These are fearful, old-fashioned and put-upon people with short fuses and the production does well to keep the audience watching their every move.

In a production originated at Stuttgart Opera, co-directors Jossi Wieler and Sergio Morabito make the most of what is a two-hour extended crowd scene polarising around the idealistic prophet and his more pragmatic sibling. Where are we? Well, the setting for both acts resembles a city council chamber vacated for the day by the burghers. (One hesitates to call it a debating chamber: there was nothing democratic about the ruling Pharoahs. But modern-day political 'Springs' in the Middle East and their aftermaths make you wonder.) Security must have been lax. But in fact it symbolises the people’s bondage by governance; their domicile is a wasteland wherever they are. You have to use your imagination.

Lots of things happen within the crowd as individuals, such as Richard Wiegold's Priest, draw attention to themselves for various reasons to do with how Moses and Aaron are interpreting their idea of a mysterious god beyond description and beyond the conventional intermediary links of idol-worship and blood sacrifice.

The coup de théatre occurs when the famous sacrifice and orgy scene is presented as a film watched by the agitated crowd, which is turned on by it. There's a lot of re-interpretation - no staff turned into a serpent; a glass of Nile water turned to blood by Aaron with the help of some schoolboy trickery. Today, only Hollywood would convey miraculous events literally, though even the big studios are cash-strapped. But Moses ripping up the Commandments bequeathed to him on the mountain top as a printed book is less impressive than a fearsome figure smashing tablets of stone. All these events, including the orgy scene done directly instead of voyeuristically at one remove would be for Hollywood, and Hollywood of the era when Schoenberg lived in the States as diasporan Jew in flight from Nazi Europe.

John Tomlinson as Moses is magisterial and Le Brocq brave and confident in a production as much about the difficulties of being a political leader among a tired and emotional people as anything else. Often, as in Aaron's water-to-blood spoof, you have to take your people for a bit of a ride. Tomlinson, uttering his sprechstimme lines like a Wagnerian bass temporarily deprived of a melody is simply definitive. Le Brocq would probably relish the opportunity to improve on a performance that understandably often had its eye on conductor Lothar Koenigs's cue-ing hand; his bel canto lines also lost some of their attractiveness towards the end. But what the heck? He's a real pro. The WNO orchestra under Lothar Koenigs plays the serial score with passion and the chorus everywhere comes into its glorious own as actors as well as singers.

Moses and Aaron is not a masterpiece in the Verdian dramatic sense but at almost 85 years old it still has the power to astonish. That says a lot about today's audiences, almost as unadventurous and as uncertain about musical sounds as the wobbly Israelites of yesteryear were about the nature of God and the power of his delegates to lead them to the Promised Land.

It was good to hear Pountney's disembodied voice welcoming the audience to the show and then see him 'live' at the side of the stage. He's transformed this company. I've been covering WNO since the 1970s and, apart from some landmark productions, have never known such an extended period of sheer innovation and excitement. Long may it continue.