Here was a night of a thousand delights, but an unhappy heart. The 67th Aix Festival got off to a hot, heady start with Katie Mitchell's witty and ingenious staging of Handel's 1735 sorcery opera, a synthesis of drama and fantasy that expands upon brief episodes in Cantos vi and vii of Ariosto's Orlando furioso.

From Anna Prohaska's opening aria as Morgana, sung while minions were strapping her to a bed in 50 shades of bondage, we knew we were in unsafe hands. (Although it probably does the lungs good to sing when you're spreadeagled). The da capo ornamentations were teased out of her by the ticklish ministrations of Anthony Gregory's Oronte, complete with a deft placement of his feather duster to trigger the money note.

All too much? I feared so at first but Mitchell won me over. This scene was a clever manoeuvre, the first of many in a masterclass of Handelian stagecraft, because it grabbed the audience's eyeballs and put them on the alert for what turned into a beautifully paced and realised production.

Before long Alcina herself was centre stage, less spicy in her sexual tastes than her sister though no less hungry. And who's that in a dingy antechamber, idly combing her beaver? Morgana again? But she's so old!

The director and her designer, Chloe Lamford, have revisited the visual aesthetic of Written on Skin three years ago in order to create an unnerving palace of illusion and secrets. There are five rooms on two levels, with an enchanted boudoir at the centre where a pair of raddled old witches can be young again (in a conceit of Mitchell's invention) thanks to a magic elixir. Upstairs there lurks a gadget that looks for all the world like an airport luggage screening belt, though its true properties turn out to be somewhat more transformative. For the rest, expect all the trademark tics: widescreen stage, supernumeraries in drab frocks and lashings of extreme slo-mo. They've never worked better than here.

Alcina relates the fantastical tale of a sorceress who lures men to her court then transforms them into flora and fauna – hence the beaver. Handsome Ruggiero is next on her list, but his beloved Bradamente has arrived to save him disguised as her own brother and, together with her governor Melisso, to right all the wrongs.

Into this unseemly environment steps a young boy, Oberto, played with breathtaking musicality and projection by 12-year-old Elias Mädler (in a role he shares with fellow Tölzer Knabenchor chorister Lionel Wunsch). He should be snapped up to sing Miles and Yniold the world over. Oberto is looking for his lost father and that puma has a fishy air...

Philippe Jaroussky cuts a mighty fine dash as the debonair knight Ruggiero, his bright falsetto easily rising above a mid-range-dominant Freiburger Barockorchester that supports the singers with admirable sensitivity under Andrea Marcon's carefully pointed conducting. The French countertenor's yearning mezza voce delivery of “Verdi prati” is sublime, possibly the evening's vocal highlight, although there is strong competition from Prohaska's “Tornami a vagheggiar” and from Gregory's physically and vocally energetic “È un folle, un vile affetto”. Add some bell-clear, sweetly defined contributions from Katarina Bradić and Krzysztof Baczyk as the gallant rescuers and this Alcina is a feast for the ear.

Or almost. The vocal particularity of Patricia Petibon is a taste I have yet to acquire, and her performance in the title role here isn't about to convert me. It was showy to the point of showing off, as though she were loving the art in herself rather than in Handel's music. The French soprano's voice is big at the top but bland in the middle and she shuttled between those two ranges without any attempt at evenness – unprepossessing within the stave, loud and brassy above it. She treated us to one unpleasant coloratura shriek and, at the climax of “Si, son quella”, one of those white-tone moments she produces on occasion that sound like a finger tracking the rim of a wine glass. And there were elongated pauses galore: melodramatic effects that left her performance mired in self-indulgence and destroyed Handel's pathos along the way. Witchcraft indeed.