Robert Wilonsky in The Village Voice:
Once, written and directed by John Carney, is a deceptively simple movie—a narrative strung together by pop songs, but without the sheen (or arrogance) of most cinematic musicals. By day, a Dublin busker (Glen Hansard) sings Van Morrison on a street corner for spare change, which, on occasion, is swiped by old friends in far more desperate straits than he. At night, the singer switches to his own compositions, most written for the girlfriend who abandoned the guy (who has no name in the film or credits other than The Guy). A Czech girl (Markéta Irglová, billed only as The Girl) approaches The Guy and asks him about his songs. He brushes her off; she’s pretty but too young (Irglová was 17 when the movie was shot two years ago). She’s also persistent.
In time, it turns out this Girl selling flowers to strangers for loose coins is also a musician—a pianist and singer, every bit The Guy’s equal. And so theirs becomes a friendship and partnership—though not quite a relationship, because of The Guy’s ex and The Girl’s estranged husband. He teaches her his songs: He gives them heart, but she gives them soul.
More here.