L'Incoronazione di Poppea, Glyndebourne Festival, Glyndebourne

One of the many delicious conceits of Busenello's ground-breaking libretto for Monteverdi's L'Incoronazione di Poppea is a kind of "reality theatre" contest between the allegorical figures of Fortune, Virtue and Love. In his wonderfully lucid and unflinching staging, Robert Carsen tops Busenello's conceit with one of his own.

As the prelude to the opera unfolds one exquisitely pained suspension after another, a sequinned lady clutching a programme pushes her way along the front row of the stalls, loudly claiming – in English – that someone is in her seat. That someone is a nun, and now we've realised that the opera has in fact begun, we can identify those responsible for the disturbance as Fortune and Virtue. Whereupon the sumptuous crimson theatre curtain does not rise but collapses in a heap to the floor to reveal... an audience just like us, waiting for the drama to unfold.

This is where Love makes her entrance, dapper in her crushed velvet suit and brandishing Cupid's arrow. She will, she promises, win the day, and since only we can see her as she sets about manipulating her protagonists in their ruthless ambitions, it's fair to say that Carsen wants us to look at ourselves and, yes, not feel too comfortable about it. So this is not a Roman Poppea but a cleverly stylised contemporary take on one.

Perhaps the biggest challenge for producers of this extraordinary piece is to prepare an edition that reveals the nuancing of the text. They must do so, however, in such a way as not to leave the audience feeling that they are wading through great swathes of recitative in the hopeless search for an aria. Every line is an aria.

And the wonder of conductor Emmanuelle Haïm's work here with the Orchestra of the Age of Enlightenment is the way she illuminates the play of Monteverdi's expressive vocal lines with the harmony beneath. There are exquisite dissonances everywhere; the modernity of it is quite startling. A single word – "Addio", as Nero leaves Poppea's adulterous bed in their first scene together – is filled with longing for the next time. And the range of colours that Haïm has devised for her continuo group (barely indicated in the surviving scores) shifts and intrigues and exhilarates with every turn of the drama. So, wonderful work from her.

Visually speaking, it's a very spare show. Carsen and his set designer Michael Levine have devised a simple visual metaphor of crimson drapes, whose shifting configurations take us deep into Nero's corrupt empire and the cocoon-like bedchamber at the heart of it. Crimson bedcovers also suggest the cloak of power that Poppea so desires.

The big turning point in the drama is the murder of Nero's learned tutor, Seneca (the gravely charismatic Paolo Battaglia), which Carsen, true to Monteverdi's inspiration (and Haïm's realisation in dancing recorders and percussion), welcomes as a joyous release on a stage strewn with his books and flooded with the light of eternal wisdom. But Carsen's real kicker is the scene that follows. As Seneca orders the bath in which he will die, Nero and his carousing male enforcers celebrate his passing with a bathing ritual of their own. One of their number is stripped and drowned while Nero plants the kiss of death on his lips. It's a shocking act of sexual sadism that points to the future of the royal union and to Nero's abuse of power.

The wonderful Alice Coote inhabits the tyrant's skin with chilling ease and considerable vocal aplomb, while the jaw-droppingly sexy, though vocally questionable, Danielle de Niese increasingly suggests that her real lust is for Nero's power. Once crowned Empress, she refuses to allow Nero to divest her of her royal robes. Their voices ecstatically entwine, but already they are drifting apart. Happily ever after? I don't think so.

To 4 July (01273 813813)