Another of Leigh's trademark British slices of life, the result of working with his cast for months in improv workshops in order to develop fully lived-in, realistic characters. This time, Happy-Go-Lucky follows a 30-year-old Londoner named Poppy (Sally Hawkins) who is thoroughly unflappable in her optimism no matter what.

Leigh gauges our tolerance for such an exuberantly cheerful person early on: shortly after Poppy fails to engage a surly bookshop employee in conversation, she finds her bicycle stolen and says simply, "Oh no! I didn't even have a chance to say goodbye!" Thankfully, this is as unbelievably Pollyanna-ish as Poppy gets – Leigh's no sentimentalist. Nor is he a sadist: an endlessly giving character like Poppy would be a sacrificial lamb in a Lars von Trier film, but while Leigh does examine the downside to being unconditionally nice, he does so without melodramatics. It's truer to reality, and truer still to his characters.

Hawkins is wonderful, but the whole cast is great, especially Alexis Zegerman as Poppy's gruff but lovable roommate and Eddie Marsan as Scott, Poppy's driving instructor, possibly the angriest man in England. The interaction between Poppy and Scott drives what little narrative the film has, and it's a pleasure to watch these two actors together.

What Leigh does is interesting in that most of the characters in the film are teachers of some sort. (Poppy, unsurprisingly, teaches little kids.) I'm still not entirely sure of the relevance here; perhaps Leigh sees teachers, whether happy or frustrated, as idealists. Indeed, Happy-Go-Lucky is about the bravery it takes to be an idealist, to be optimistic in a world that is anything but. (The film is shot in London's dullest neighborhoods, which emphasizes the difficulty of maintaining a joyful spirit in a place so devoid of character.)

I found this film both thought-provoking and inspirational. As one critic said of Poppy, Leigh the Utopian sees her as the next evolutionary step for humankind; a woman out of place in 2008, perhaps, but a harbinger of what's to come. To call Happy-Go-Lucky a "feel good" movie would be dismissive; it's a real drama, with complex characters and a sense of darkness. But in reminding us of our shared responsibility in making the world a jollier place, it's the sweetest, perhaps most important film of the year.