It seems to be a truth universally acknowledged in film that self-destructive addicts are an easier sell when they’re easy on the eyes. (Pretty people just look so much better retching, screaming, lying and relapsing.) Hence we had Matt Dillon in Drugstore Cowboy, Jared Leto and Jennifer Connelly in Requiem for a Dream, Heath Ledger and Abby Cornish in Candy, and now Anne Hathaway in Rachel Getting Married. Luckily, casting a gorgeous actress as a highly unattractive character was one of the few predictable decisions director Jonathan Demme made.

Hathaway plays Kym, an ex-model who’s struggled with drinking, pill popping and eating disorders since her teens and has settled into a groove as the Problem Child in her well-off, well-meaning suburban family. Rosemarie DeWitt is her sister Rachel, the one who’s getting married; the film opens with Kym’s father and stepmother (Bill Irwin and Anna Deveare Smith) springing her from rehab to attend the wedding. In the film’s first lines, we learn that Kym once killed someone at the wheel. Though screenwriter Jenny Lumet (Sidney Lumet’s daughter) takes her time revealing who died, the painfully awkward, frozen-faced reception Kym gets from her mother (Debra Winger) suggests the casualty was in the family.

All this sounds like material for a modern-day Ordinary People. But Demme’s characters aren’t a bunch of repressed WASPs. They’ve talked everything to death and “dealt with” their grief, to the extent such things can be dealt with. Using handheld camera work, the director plunges us into the family’s intimate life; he zips up and down stairs and whip-pans from person to person as their conversations fill with in-jokes and still-raw sorrows and polite lies. This ultra-realist technique — reminiscent of Robert Altman — can be disorienting, but the complex, sinewy writing and acting make it work.

Take Irwin, who plays the paterfamilias as one of those relentlessly sunny small-town-anchorman types. But the character isn’t dim or naïve, and when he breaks down, the audience comes with him.

Or take the relationship between Kym and Rachel, which initially comes off as a straight-faced version of Sarah tormenting her sister Laura on “The Sarah Silverman Program.” Rachel seems earthy, love-addled and a bit simple, while nasal-voiced Kym runs around goading her and generally being outrageous. (Her idea of a compliment: “You’re so skinny, I could swear you’d started vomiting again!”) But after Kym makes the wrong toast at the rehearsal dinner, Rachel shows she can wage family warfare as fiercely as anyone.

The film’s main event, though, is the match-up between Hathaway and Winger, who hasn’t been on-screen much since the mid-1990s. Her face has changed, but her throaty voice hasn’t, and when she drops the social mask and lets her rage rip, you wouldn’t want to be in Kym’s place. Though her explosion is brief, it’s no mere Oscar grab.

Nor is Hathaway’s performance. She plays Kym as a precocious, self-centered, emotionally transparent child, a girl who matured early but never really grew up. Tears come to her eyes as she listens to other people’s woes at her AA meeting, but that sensitivity doesn’t stop her from cornering her family members in inventively cruel ways. She’s the attractive narcissist we’ve all known, the one you can’t quite hate because her directness and energy keep life moving.

If the movie has a flaw, it’s that Kym’s character doesn’t develop so much as flail. Things are hashed out and truths are spoken, but it’s unclear if anyone will be the better for it. Instead of taking their characters on a traditional path through conflict to resolution, Lumet and Demme do something unusual: They juxtapose the conflict with pure and simple joy. Ultimately, the film is about Rachel’s wedding, and that wedding is interracial and multicultural, full of colorful costumes and live music in all genres and laughter and genuine affection. (It’s like the visions of America’s future a lot of us had on election night.)

Back in the ’80s, before he won Oscars, Demme directed some great romantic comedies with infectious, eclectic soundtracks, and he returns to his roots here. Rachel Getting Married definitely isn’t a comedy. But it’s the happiest movie about a severely dysfunctional family you’re likely to see.