Gounod's Roméo et Juliette isn't exactly a rarity, but it is no longer one of the stalwarts of the opera repertoire, a position which it certainly occupied during the Victorian era (there were 102 performances at the Théâtre-Lyrique in Paris in the first year of its life, followed by 291 performances at the Opéra-Comique in the next twenty). The Royal Opera's present production dates back to 1994, and is being revived for just the second time.

Gounod lived in the shadow of Wagner: he has been criticised both by traditionalists for being too much like Wagner and by modernisers for failing to push the harmonic and stylistic boundaries of opera in the way that Wagner did. But viewed from the safer distance of a few years, the score is glorious. Gounod has a marvellous knack of matching the music to events and picking up the moods and emotions of his characters, even when these are changing rapidly through the scene. Whether it's playfulness, romance, anger or stern authority, the music puts you precisely in the state of mind of what's happening on stage. And while the score may lack a level of cohesion or sense of overall progression, it is full of moments of intense beauty. Last night, conductor Daniel Oren provided us with a subtle and beautifully balanced rendering, beautifully complementing the singers (and never overpowering them) while strong and colourful in the instrumental passages.

Last night's singers were melodious and expressive throughout. Piotr Beczala's Romeo was outstanding: he has a warm timbre and gives you the sense that the music flows easily. It's a big part: Romeo is on stage singing for a large proportion of over three hours of music, and I could have carried on listening to Beczala all evening. I thought Nino Machaidze took a while to warm up as Juliet: she sang her Act I blockbuster Je veux vivre with panache, but the voice was harsh around the edges. By the time of the Act IV duet in which she forgives Romeo for Tybalt's killing, it had all smoothed out, and she was a delight to hear. The supporting cast was strong: Stéphane Dégout and Alfie Boe were lively as Mercutio and Tybalt. But my favourite moment of the evening was from a strange little cameo: Romeo's page Stéphano (a mezzo trouser role) comes on to sing Que fais-tu, blanche tourterelle?, in which he taunts the Capulets that their beautiful turtle-dove is about to flee their nest of vultures. It was sung by the Georgian mezzo Ketevan Kemoklidze, and it brought the house down.

What lets the opera down - and makes it an OK work rather than a great one - is Jules Barbier and Michel Carré's libretto. The overall flow follows the Shakespeare story closely enough, taking only a few liberties. The problem is that the language is unbearably prosaic, especially if you've been brought up on Shakespeare's exquisite poetry. Translating Two households, both alike in dignity / In fair Verona, where we lay our scene as Vérone vit jadis deux familles rivales / Les Montaigus, les Capulets simply isn't good enough. By the time the words have been hacked down into English surtitles, they're worse, and unfortunately, I was forced to read the surtitles even though I'm a bilingual French speaker. The singers' diction was dreadful throughout, especially in the chorus where you could hardly make out a consonant in the entire evening. They made a beautiful sound, particularly in the religious passages at the beginning and in the wedding scenes, but the words had gone AWOL. With the obvious exception of Stéphane Dégout (who is French), I suspect that they had trouble with the language: in the period since Bachtrack started, the Royal Opera has given five times as many performances in Italian as in French. Piotr Beczala provided a moment of great hilarity for any French speakers in the audience by announcing to Juliet that he had "drunk the fish" by softening the z sound of "poison" into the sibilant s of "poisson".

The stage direction didn't help. The sets were fairly basic and the costumes fairly traditional (Romeo's two-tone effort seemed to have stepped out of a Commedia dell'arte rather than a Veronese palace, and the movie title "Robin Hood - Men in Tights" kept creeping into my head), but mainly, it's that the whole thing was rather static. The fight scenes were well directed, but there was little dynamism in the interplay between characters. Even at the critical moment of Juliet's collapse at her wedding, Paris and Lord Capulet stood firmly on the spot as they sang, with no attempt to rush towards their fainting loved one.

The libretto's failings and a lacklustre production mean that Roméo et Juliette isn't going to go down as one of Covent Garden's hits of the season. But it's still an evening of lovely singing and gorgeous music. Gounod may not have been a radical or innovative composer, but he produced some real vocal and orchestral magic, and both singers and orchestra did it good justice at Covent Garden last night.