I Was Looking at the Ceiling and Then I Saw The Sky, Theatre Royal Stratford East

John Adams thinks his and poet June Jordan's fantasia on love in a time of earthquake flopped at its 1995 Berkeley premiere for two main reasons.

The characters - three blacks, two whites, a Hispanic and an Asian - were deemed too self-consciously multiculti: odd when America knew that was just how LA was then, even more so than Stratford East today (for once, the audience reflected the cast in this co-production with the Barbican). And Adams was shocked to find the pop and classical worlds so rigidly defensive. I've spoken to plenty of folk who hate the piece, trapped as they are behind the barriers its 24 vernacular numbers try to break down. Yet it seemed no problem for anyone in the theatre last night, chiefly because the ensemble of seven brilliant young singer-actors was totally on top of their tricky music. They'll never have to master anything as complex again, so they have every reason to be proud.

Whether it works as total music-theatre from start to finish is another matter. It's a bold idea to tell the drama entirely through the string of elaborately treated pop song stylisations, from Motown and gospel to rap and hip hop. But the interwoven lives of seven twentysomethings living in Northridge, the epicentre of the 1994 LA earthquake, aren't clearly introduced and take some time to find their proper context. We're told, very wordily, where the sexual, racial and political conflicts lie, but as the cataclysm isn't scheduled until some way into Act Two, you wonder where it's all going. And though the final number in Act One is the ravishingly beautiful "Alone (Again or at Last)", sung by philandering preacher David's girlfriend Leila - the marvellous and adaptable Cynthia Erivo (pictured below with Jason Denton) - it's no torch song, so inevitably it makes an odd curtain.

Still, the pace is varied and swings from the vibrant "Solo in Sunlight" - high noon for the sexy-charismatic Dewain of Leon Lopez before everything goes wrong - to two bittersweet numbers for El Salvadorean refugee Consuelo. I can't get the sound of the superlative Audra McDonald on the original cast album out of my head, but Anna Mateo is even more authentic, and she handles very affectingly the wonderful harmonic shift as buildings topple in her dream of Mr Right (shades of Pat's transcendental solo in Nixon in China, and hints of the Latin American complexities to come in El Niño). There's gritty humour, too, as the three ladies tell us how "when there's the bad boys, bad news can't do nothin' bad to me". It could be arch, but it's superbly staged by Kerry Michael and Matthew Xia with the men increasingly uncomfortable on the margins as the women get ribald. The staging's simple - only seven chairs and a water-cooler for retreats in Act One, destruction stripping everything to a back wall and Tal Rosner's discreet video projections in Act Two.

Come the earthquake, and you see the symbolism: the characters have been looking at the ceiling, with racial tension between the white police officer and anchorwoman on the one hand and their respective objects of desire, Dewain and Vietnamese-American Rick (Colin Ryan), on the other, but now they see the sky. This is where the polyphonic lines are most skilfully woven and fluent speech-melodic writing becomes more operatic. A dramatically skillful trio and an ensemble, part of Adams's rewrite after the premiere, seal the shift.

Stewart Charlesworth and Natasha J Barnes complete the line-up as the ill-matched white couple driving around the mean streets; they put across their numbers as well as anyone in a cast without a weak link. And the moody pit band goes much further than its mostly Finnish counterparts on the original recording conducted by Adams. Here we have haunting clarinet riffs from Lucy Downe in Rick's counsel-for-the-defence solo and Sam Healey's sax impros go wild against often violent choreography by Jason Pennycooke. We'll never know how hard music director Clark Rundell must have worked on getting the co-ordination perfect, but perfect it was last night. I only hope Adams, who says that this one-off score in his output contains some of his favourite music, got to see it.

• Further performances at Stratford East until 17 July
• John Adams's El Niño in concert at the Edinburgh International Festival
• Buy the original cast recording on Amazon