When Gershwin works, it works with a vengeance. At English National Opera last night, when Latonia Moore sang of Old Man Sorrow coming to keep her company in “My man’s gone now”, we felt every inch of Serena’s grief for her murdered husband as well as admiring the extraordinary lyrical beauty of the music and the remarkable voice that was singing it. When Nmon Ford’s Crown, the bullying braggart who is the murderer, traps Nicole Cabell’s Bess on Kittiwah Island, the moment is deeply disturbing, as is the way in which Frederick Ballentine’s drug dealer Sporting Life finds it all too easy to seduce Bess, late in the opera when Porgy is in jail.

ENO’s first ever production of Porgy and Bess – it’s wonderful to see them do it, if shameful that it’s taken this long – unites James Robinson’s watchable, credible staging with consistently excellent acting and mostly excellent singing. But it’s Gershwin’s music that wins out, played quite brilliantly by John Wilson and the ENO Orchestra. Wilson is vibrant in the exciting parts, folksy in the spirituals, achingly romantic in the love songs, violent in the storms and fights. But what strikes you most is how much subtlety there is in the music. “Summertime” may be the most covered song ever (with over 25,000 recordings), but it’s so much more than a famous melody: the real magic is in the way that melody is interwoven with sinuous contrapuntal accompanying lines. The final trio, in which Serena and Maria fail to persuade Porgy to make the hopeless trip to New York in search of Bess, is worthy of any 20th-century master of opera composition.

Both title roles are tricky. Porgy is a contradiction: physically, he’s a severely incapacitated cripple and a beggar. Musically, he is a tower of strength. Eric Greene turns in a barnstorming performance which succeeds admirably in riding both horses: a strong, appealing voice combined with lashings of stage presence, somehow managing to survive three hours on stage with his foot horribly twisted to make the disability credible. We believe utterly that such a man can be a paragon of constancy and resolve. Bess is a character riven with inconsistency: a woman who likes the idea of being good and settled but isn’t strong enough to resist the sexual allure of Crown or the narcotics of Sporting Life. Cabell acted the role superbly, making us sympathise with Bess as well as furious at her inability to do the right thing. However, I’m not sure her voice is right for the role, the projection from the back of her vocal tract giving a slightly odd timbre and a lack of clear diction. Similarly, Ballentine’s acting was top class, making Sporting Life horrifically creepy, but I wasn’t taken with his decision to speak and whoop a great deal of “It ain’t necessarily so” rather than fully voice it.

Porgy and Bess is an ensemble opera with a lot of main roles, and apart from those two cavils, the singing cast did full justice to the music. Moore was the pick of the singers, but Nadine Benjamin (as Clara) gave us a creamily smooth rendition of “Summertime”, Tichina Vaughn gave excellent support as Maria, and I could easily have name-checked most of the others. The big spiritual choruses were sung thrillingly.

Michael Yeargan’s sets are effective, consisting of timber framed buildings that shift around smoothly to show us a variety of different aspects of Catfish Row; scene changes are handled adeptly behind a screen which displays intelligent video projections laden with black and white photography of the period. There’s the occasional misfire: the video-projected rainstorm is sadly anaemic (especially when set against Gershwin’s virtuosic storm music), and something during a scene change caused a foot injury to Nadine Benjamin – I hope it’s not as serious as it looked and that she recovers quickly.

Porgy and Bess isn’t a perfect opera. There’s plenty of wonderful musical material to fill its three hours, but there isn’t enough plot: basically, it’s “While Crown is on the run for murder, his woman Bess takes up with the cripple Porgy; when Crown returns to claim Bess, Porgy murders him; while Porgy is in jail, Bess leaves.” There’s more detail than I’ve just given you and a few interesting subplots, but too much of the opera is spent adding local colour and not enough driving the action forward. However, the musical richness is so great that it carries you through. With all the covers of those famous songs, it’s easy for us to form a picture of Porgy and Bess as some sort of jazz opera. That's simply wrong-headed: the reality is a far more coherent and nuanced work, of which this production is a thoroughly enjoyable exposition.