For the third of their major operas this season, the English National Opera chose Mozart's Idomeneo, one of Mozart's earlier masterpieces telling the story of the Cretan King Idomeneus's homecoming after the Trojan War. To allay the wrath of the sea god Poseidon, Idomeneus has made a rash vow to sacrifice to him the first person he sees upon landing: disaster engulfs him and Crete when this turns out to be his beloved son Idamante. The ENO put on an all-new production from director Katie Mitchell.

Mozart was blissfully happy when writing Idomeneo, and it's easy to see why. While the music may lack the transcendent quality of some of Mozart's later and more famous operas, Mozart's energy and inventiveness leap out at you from every line, and the opera is a showpiece for Mozart's unique ability to create ensemble pieces where voices and orchestral instruments collaborate and intertwine. Some of the writing for woodwind and voice is quite unspeakably beautiful.

As in Tosca a few weeks ago, I couldn't fault Edward Gardner's conducting. The orchestra delivered energy, drive, instrumental quality and perfect balance throughout the evening. Vocally, the cast matched them for quality from the beginning. The opera opens with the Trojan princess Ilia mourning her captivity and her inappropriate love for Idamante in a recitative and aria in which she holds the stage single handed for what seems like an impossibly long time. It has to be a stern test of any soprano, and Sarah Tynan carried it off impressively. Emma Bell's desperate, furious Electra was sung with such fire that it was difficult to imagine how Idamante could resist her. The male roles - Paul Nilon as Idomeneo and Robert Murray as Idamante - were perhaps a shade eclipsed by the soprano's virtuosity, but still sounded wonderful, with Nilon's Handelian colorotura delivered with some style. Also, I thought Adam Green's one main aria as Arbace was an unexpected highlight. And the chorus in Act III as the Cretans discover the nature of Idomeneo's vow knocked me for six.

If this had been a concert performance of the opera, I would have given it ten out of ten. But it wasn't. And the production, I'm afraid, gets a very definite thumbs down.

I'm not against modern productions of ancient stories: the ENO's Pearl Fishers worked brilliantly. But the choice of setting in this production was nothing short of bizarre. We seemed to be set in a standard business hotel - a Hyatt Regency or a Hilton, perhaps. The main characters barely moved around the stage or interacted with each other at all: rather, they engaged in heroic bouts of drinking as a succession of waiters moved across the stage refilling their glasses and serving them with meals. It was as if the director didn't trust her singers to hold the audience's attention, and felt that something else needed to be done: the problem is that the something else was all about taking my attention away from the singing and the drama, rather than doing anything at all to enhance it. The weirdness increased in Act III, when in Ilia's desperate and beautiful aria asking the "amorous breezes and lovely flowers" to listen to her plight, we were expected to watch a projected video of what looked like a steadicam shot of Kew Gardens, complete with hotel flunkeys coming in to mend the projector as Ilia's face was half in darkness. And I'm afraid that some ripped curtains and a fallen pine tree in the hotel lobby definitely weren't enough to give me a feeling of Crete devastated by storms.

The translation didn't help, particularly in the case of Electra. Lines that were reasonably poetic or at least neutral in Italian were turned into banal prose (example: "I'm so angry"), which elicited raucous laughter from the audience. I somehow doubt the comic relief was intended - after all, Mitchell's conceit is that Electra actually shoots herself at the end of the opera, rather than simply storming off.

Once a production has started to wind you up like this, you start noticing a million small irritations, and I'm not going to list them all. And I have a certain amount of sympathy for the director. The principle of Greek drama, as mirrored faithfully in this opera, is that the audience knows the story in all its details before entering the theatre. Therefore, the interest lies not in the action but in the poetry and the characters' motivations and reactions. Clearly, it's a difficult task to render this style on a modern stage for audiences who are not well versed in its traditions. But when all is said and done, I felt that events on stage were detracting from a wonderful piece of music, which is rather losing the point of going to the opera.

None the less, the music is quite glorious. Go to hear this production, if not to see it.