Lisa Cholodenko's The Kids Are All Right (Focus Features) is the movie we've been waiting for all year: a comedy that doesn't take cheap shots, a drama that doesn't manipulate, a movie of ideas that doesn't preach. It's a rich, layered, juicy film, with quiet revelations punctuated by big laughs. And it leaves you feeling wistful for at least three reasons: because of what happens in the story, because the movie's over, and because there aren't more of them this good.

Jules (Julianne Moore) and Nic (Annette Bening) are a middle-aged lesbian couple in Los Angeles with two teenage children, Joni (Mia Wasikowska) and Laser (Josh Hutcherson). Nic, a physician, is the breadwinner of this stable, well-off family, while the unfocused Jules has vague plans to start a landscaping business on her partner's dime. Near the start of the movie, Joni, at her younger brother's urging, calls up the sperm bank that provided their mothers with genetic material 18 years ago. Behind their mothers' backs, the siblings make contact with their hitherto anonymous biological father, Paul (Mark Ruffalo), a hedonistic restaurateur who's flattered by the attention but unsure how to proceed. Gradually, Paul is incorporated into the fringes of the family: The children bring him home for an excruciatingly awkward lunch, and against Nic's wishes, Jules takes on the job of landscaping his yard.

It's fitting that gardening—Jules' landscaping project, Paul's achingly trendy farm-to-table restaurant—plays such a large role in The Kids Are All Right, because the movie is at heart about the ecosystem of a family, and the way that system changes when an exotic species is introduced. The presence of Paul changes everything, exposing fault lines in Nic and Jules' relationship and forcing the children to defy their mothers and reassess their peer friendships. (A subplot in which the introverted Laser finally stands up to his jerky best friend is particularly well-handled.)

In one of the movie's funniest scenes, Nic unleashes her hostility toward Paul in an icy diatribe about the organic-food fad: "If I hear one more person say how much they love heirloom tomatoes, I'm going to punch them right in the face." Without ever making the comparison outright, Cholodenko and her co-writer Stuart Blumberg draw a parallel between the aspiration for organic purity and the myth of the perfect family. However assiduously you cultivate your garden, they suggest, there's no predicting what might crop up by surprise or how it'll grow.

In a movie whose story hinges entirely on how the characters treat one other, the acting here is really interacting, and this stellar ensemble cast gets it exactly right. Bening makes Nic a force to be reckoned with: an acid-tongued workaholic who loves her wine a little more than she should but who's such lively company you understand what Jules sees in her. A scene in which Nic sings Joni Mitchell's "All I Want" a cappella at a dinner party veers from embarrassment to exaltation—and then back to embarrassment again.

The ever-astounding Julianne Moore finds lots of layers in Jules: passive-aggression, vulnerability, coquettish vanity, sexual hunger. Ruffalo just Ruffaloes it up, playing the kind of part that's been his subspecialty since You Can Count on Me: the immature but well-meaning and rakishly sexy scamp. And as the kids who aren't always, but eventually will be, all right, Wasikowska and Hutcherson are tentative and tender and convincingly sibling-like. The scene in which the family drops the college-bound Joni off at her freshman dorm will wring tears even from the few audience members who made it dry-eyed through Toy Story 3.

More than anything, The Kids Are All Right is a film about marriage. Not about gay marriage in particular, though the portrait of this couple's decades-long bond underscores the absurdity of the debate about what to call same-sex unions. Cholodenko, who has a donor child with her partner, isn't making a rah-rah commercial for alternative families—in fact, some gay viewers may bristle at the movie's less-than-orthodox take on lesbian sexuality and the complications of donor parenthood. What Cholodenko has aimed for, and achieved, is something bigger: a serious and funny film about the simple yet incomprehensibly fraught act of moving through time with the person you love.

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