Rameau's Castor et Pollux, his take on the Greek myth of two brothers so close that Pollux is prepared to descend into hell in the place of Castor, isn't exactly one of the standards of the repertoire. But Barrie Kosky isn't exactly an ordinary director: he's an Australian who has made most of his opera career in Germany and is on his way to a new job as Intendant of the Komische Oper Berlin, something of a temple of the avant-garde. And to judge from the interview in the programme notes, Kosky knows his Rameau backwards, forwards and sideways.

The prime intention of the production was to "let the music breathe", and in this, it was an unqualified success. Under the baton of early music specialist Christian Curnyn, the ENO orchestra were delicate, clear and beautifully balanced with the voices (my last outing to the opera made vividly clear how an evening can be spoilt by lack of balance). Rameau may have been a contemporary of Handel's, but his musical style is worlds apart, with more complex orchestration, little in the way of big set piece or da capo arias and a blurring of the boundaries between recitative and aria (students of opera would call his operas more "through-composed"). It makes for an opera that is far less flashy and far more of an ensemble piece than Handel's vehicles for star singers to wow their audiences.

But with or without showy music, the ENO's quartet of main singers were superb. Sophie Bevan was exceptional as the beautiful sister Telaïre, with clear high notes and delightful phrasing. As the supposedly ugly sister Phébé, Laura Tatulescu projected the forces of darkness vividly and with power. As Pollux, Roderick Williams projected royal nobility and genuine goodness with a lovely timbre - another of those voices I could sit back and listen to all evening. If your measure of a great tenor is his ability to nail loud high notes in the middle, you won't have liked some bad moments from Allan Clayton as Castor. Ignore those, however, and Clayton was marvellous, with a voice that was warm and effortless. Amongst the supporting cast, Ed Lyon made an entertaining Mercury, clad in business suit, trilby and the most glorious set of gently waving feathered wings.

All the singers showed great diction, for which a fair chunk of the credit must go to translator Amanda Holden. For the first three quarters of the opera, the metre of the English words tightly matched the phrasing of the music - no clever linguistic tricks, merely simple, poetic language chosen perfectly for its purpose (the last quarter wasn't as good, leading me to speculate, perhaps unfairly, that Holden had to rush to meet deadlines). I have distinctly mixed feelings about seeing opera in translation, but I would have few qualms at all if the translations were always of this quality.

Kosky's staging was nothing if not innovative, with dozens of individual directorial conceits. Some of these I found brilliant, some were quite good fun and some went completely over my head; I suspect that anyone who goes to this production will have a similar reaction, but with a different selection of what worked for them and what didn't. The central conceit is of people being (literally) boxed in to their world - be it earth, the gods' paradise of Olympus, the humans' paradise of the Elysian Fields or the less happy parts of Hades. An amazing trick saw characters moving through actual mounds of dirt as they travel between earth and the underworld. In another notable effect, when the brothers have been raised to the stars, twin showers of stardust cascade down onto the shoes they have left behind. And Kosky deals brilliantly with the thorny problem of Rameau's interminable dance numbers that intersperse the action: there's no actual ballet in this production, but an enormous amount of vigorous stage movement illuminating the thoughts of the characters.

For the most part, the bits of the production that left me baffled were Kosky's erotica. While I had no problem with the lovers Castor and Telaïre being unable to keep their hands off each other for the first half of the opera, I struggled horribly to follow Kosky's vision of Olympian paradise as a place in which girls in pastel dresses and white pop socks continuously drop endless pairs of knickers but never "go all the way", contrasting with Elysium as a place in which girls in similar pastel dresses and white pop socks drop endless pairs of knickers and proceed to parade around the stage stark naked, mostly turning out to be men. And when Phébé is singing of how she is going to tame the fires of hell, I truly failed to see the point of the disembodied hand which emerged from the mountain on which she is leaning to enthusiastically masturbate her throughout the aria. I can only muse on the perils of being square, the mixed blessing of being a female opera singer and that erotica are the most personal of directorial conceits, in which the phrase "to each his own" applies more than anywhere else.

But when all is said and done, my test of a great opera production is whether the director really loves the music and is able to make that love shine through, and for this, I give Kosky, Curnyn and the ENO three cheers. I may have been lost by some of the production details and I might have wished for a specialist baroque band with just a little more bite, but we were treated to a fine exhibition of Rameau's music, an excellent display of singing and a carefully honed projection of the opera's central message: regardless of the joys or sorrows of heaven, hell or earth, true brotherly love does indeed conquer all.