Sean Penn shines as gay rights activist Harvey Milk in Gus Van Sant's new drama

On Nov. 4, same-sex marriage advocates suffered a setback when Californians narrowly passed the Proposition 8 ballot initiative ensuring that the state would only recognize marriages between men and women. The biopic Milk screened in Atlanta three days later, and its portrait of gay activism and California politics feels almost shockingly immediate, despite taking place three decades earlier.

Oscar winner Sean Penn plays Harvey Milk, a pioneering gay rights advocate who challenged hostile attitudes and institutional oppression, most notably Proposition 6, a California ballot initiative designed to fire schoolteachers suspected of being gay. In some ways Milk proves to be a tame, conventional film biography, but the post-Prop 8 climate gives it an urgency and relevance that may have been missing had it opened a month or two ago.

The opening credits evoke the era of the closet and criminalization, with black-and-white footage of gay men under arrest, hiding their faces and being crowded into paddy wagons. At the dawn of the 1970s in New York, Milk works at an insurance company and passes for straight, even though he's not too shy to beam and bat eyes at handsome strangers in the subway. He hits it off so well with young Scott Smith (James Franco) that the two decide to make a fresh start in San Francisco.

A seamless mix of archival and re-created imagery captures the scruffy hedonistic spirit of Castro Street in the 1970s. When Milk opens a camera store, however, he discovers that even the gay mecca contains bigoted businesses. He begins organizing for gay solidarity to defend against gay bashing and to flex economic muscles. A tipping point occurs when Milk makes an unlikely alliance with the Teamsters Union to boycott Coors beer. He pushes even further for gay rights by running uphill campaigns for San Francisco city supervisor.

"Big Love" writer Dustin Lance Black delivers a script that hits the familiar beats of Hollywood biopics all too predictably. At times the dialogue sounds written for trailers rather than dramatic scenes: "Harvey, what's with all this political activist crap?" "You'll be the first openly gay man elected to major office!" When people approach Milk with big pieces of news – "You need to see this!" – the scenes feel like lessons in recent history.

Director Gus Van Sant returns to his highly accessible narrative style along the lines of Good Will Hunting, in contrast to his more esoteric projects such as Elephant or Drugstore Cowboy. Nevertheless, Milk's clarity and directness give it plenty of momentum, apart from standard-issue suffering spouse scenes with Franco, and Diego Luna as Milk's subsequent boyfriend.

Penn buoys the film significantly with a surprisingly breezy performance that's almost elfin, particularly when compared to his tormented method-actor shtick. Penn brings appropriate outrage to Milk's big, angry speeches, but he's also a flirt, and the audience suspects that Milk's passion for social change went hand-in-hand with his personal charm. He cracks self-deprecating jokes in front of hostile straight audiences while tailoring more personal challenges to young gay men on the street. Milk turns apolitical party boy Cleve (Emile Hirsch) into his de facto successor when he finally wins office.

Milk builds to a more engrossing second hour as it dramatizes the battle against Proposition 6 and Christian family values fascists such as Anita Bryant (shown only in archival film). A fascinating parallel track follows the strained, perplexing relationship between Milk and fellow supervisor Dan White (W.'s Josh Brolin), a staunchly conservative Catholic family man who seems at once attracted to and repelled by Milk (who thinks he's "one of us"). Brolin gives White the awkwardness of a man who may be an enigma even to himself – a performance that's particularly powerful if you know how Milk and White's fates become inextricably entwined.

Watching Milk prompts the unanswerable question, if the film had been released in September or October, would Proposition 8 still have passed? As a prestigious drama better suited for art houses than shopping malls, Milk may primarily preach to the converted. But Proposition 8 passed by only about half a million votes, so it may not have taken much to sway some people. Milk may serve as a rallying point for a young generation of gay activists, even though it missed its chance to try to make history.