Unlike Once, Begin Again isn't structured around a budding romance between its two leads, even though sparks do fly between Knightley and Ruffalo (most notably in a sequence where Gretta and Dan take a leisurely nighttime stroll through the streets of New York, accompanied by the vocals of Frank Sinatra and Stevie Wonder on her iPod). On the contrary, the movie is all about how its characters deal with the emotional fallout from their broken relationships and, in some cases, learn how to mend them.

Half of this is conveyed (quite sublimely) in the film's songs — from the show-opening 'A Step You Can't Take Back' to the closing track, 'Lost Stars' — which are sung with down-to-earth grace and charm by Knightley and Levine and will stay with audiences long past the closing credits. Carney uses the songs to tremendous effect, allowing their lyrics to help chart the characters' thoughts and emotions, sometimes playing different renditions of the same song to convey varying perspectives or to heighten its emotional impact.

The music is complemented by the actors' performances, especially that of Knightley and Ruffalo, who fill their roles with an irresistible charm, even when their characters aren't feeling nearly their best. The two leads set a bassline for the tone of the entire film, one that's never overly melancholy, despite their relationship woes. There's always a gentle airiness about — whether it arises from Knightley's impish smile or Ruffalo's gruff, yet loveable, demeanor — and it makes the movie feel refreshing, even if the broad strokes of the story are something we've seen once before.