British musical theatre is going through a reboot. Behind the scenes, something's bubbling. The same thing happened in New York in the mid-nineties: a new generation of composers burst through off-Broadway: Jonathan Larson with Rent, John Michael LaChiusa (The Wild Party) and Adam Guettel (Floyd Collins). With revivals coming one after the other, it's almost like London's looking for tips.

Jason Robert Brown was, arguably, the crown prince of that crowd: a Tony-winner by 30 with a rare ability to cram a whole story into each song. Having broken through with Songs for a New World (revived here last year), he set a failed marriage to song in The Last Five Years – proof of his feeling for form. One partner moves forwards, first date to heartbreak. The other runs in reverse. They meet in the middle: a duet surrounded by solos.

There's not much of a plot. Jamie (Jonathan Bailey) is a novelist, whose reputation's taking off, and Cathy (Samantha Barks) is an actress, grinding to a halt. Instead, shape tells the story. It's a cross-section of love; a relationship sliced into slides and slipped under the microscope, as if someone's searching for the thing that went wrong. We can probably see it was never quite right. They're two people at a distance, both wrapped up in themselves. Each only has eyes for their audience and the only thing they do together is marry.

Elsewhere, they're at odds: one young, one older; one loved-up, one worn-down. The juxtaposition says it all: broken relationships are good times and bad, and Brown's stage image captures what makes them so painful. The memory of the person you fell at the start for co-exists with the person you've become by the end. At your worst, you think of their best.

In truth, it's more illustrative than it is emotive. Jamie and Cathy are little more than Him and Her. He's a bit self-obsessed, she's a little naïve, and that's about it. You admire Brown's intricate song-writing more than you care for his characters. You hear the beats that their hearts miss or feelings turned sour as major slides into minor. Though a tad samey, one or two numbers are brilliant: "Climbing Uphill" is a fake smile of a song about endless auditions, and "I'm a Part of That" bristles then melts back into love. Barks sings both beautifully. Bailey holds his own, though he strains for the big notes.

Brown directs, badly. He plonks each number in its real-life setting, so that beds and car-seats and Christmas trees truck on, each more plasticky than the last. Derek McLane's naff design snags on itself, but such a theatrical structure warrants an abstract staging; something to tie the whole thing together.

Instead, it feels weightless, cut off from society, and it's not. Brown is sharp on gender disparity and the aging process, and Barks blossoms back into her youth, just as the boyish Bailey grows into his years, more wise and authoritative with age. Both capture the headrush of young love, and the way life loses its colour with age, but there's a sharper critique within: that women become wives and men, successes. That hasn't changed these last 50 years, let alone five.

The Last Five Years runs at the St James Theatre until 3 December.

We popped into reheasals for The Last Five Years, watch the video below