The only thing truly surprising about Michael Mann’s Public Enemies is that it took him so long to make it. From his debut film, Thief, down through Heat, Collateral, and Miami Vice (the DayGlo TV show and the blue-black movie alike), Mann has made a career out of cops-and-robbers mythologizing. But why invent legends when the truth is even more remarkable? Why fabricate modern-day John Dillingers when you can tell the story of the man himself?

Not that the tale Public Enemies tells agrees exactly with the historical record. Mann’s portrait of Depression-era America’s most prolific bank robber, embodied by Johnny Depp, includes plenty of dramatically convenient compressions and inventions. But the lineaments of the story are true enough: Dillinger’s moll and his pals; the dozens of banks he knocked over; the two prison breaks he orchestrated; the way his depredations helped summon modern crimefighting into being; and of course his made-for-Hollywood final hours. And Mann, the bard of lawbreakers and the lawmen who chase them, is the obvious director to tell it.

The movie’s structure, inevitably, is similar to that of Heat, which featured Robert De Niro planning heists in contemporary Los Angeles and Al Pacino trying to stop him. In Public Enemies, too, there’s the gang of bank robbers, headed up by Depp’s Dillinger; the gaggle of lawmen, led by Christian Bale as G-Man Melvin Purvis; and the extended cat-and-mouse games punctuated by machine-gun exchanges. And of course there’s the love interest — Marion Cotillard as Billie Frechette — who wants our gangster hero to escape the grisly fate that his career has prepared for him.

But Public Enemies has more recessive stars than Heat — there’s no Pacino-style scenery-chewing here — and a larger canvas to work with. The narrative pulls back frequently, framing the cops and robbers in the broader New Deal era. This macro-story is all about centralization and its consequences: the power of the mass media to make Dillinger a national celebrity, the power of a young J. Edgar Hoover (Billy Crudup, prissy and brutal in equal measure) to nationalize crimefighting, and even the power of the Chicago Syndicate to nationalize crime.

Both Dillinger and Purvis, in different ways, are ground down by the gears of centralized power. When the story starts, for instance, the Syndicate has an easygoing relationship with the roving bank robbers — laundering their money, welcoming them to safe houses, and so forth. But eventually the mob turns on Dillinger, flushing him into the open for the Feds to run down. As a mid-level mobster explains, it’s too risky for a modern criminal operation to tolerate outlaws and freelancers: Even gangland has gotten a dose of that rationalized New Deal spirit.

For Purvis, what’s ground away is moral principle. When he first starts hunting the Dillinger gang, he is the one lecturing the technocratic Hoover — who’s enamored of a civilized, scientific FBI — on the need to have hard men and heavy weaponry involved. But the demands of power soon reverse that dynamic: Hoover decides that the end of catching Dillinger justifies almost any means — up to and including torture — and his subordinate is left waist-deep in a moral morass. (The moment when Hoover tells Purvis “to take off the white gloves, as they say in Italy,” is a rare one-liner capable of eliciting rueful nods from opponents of the Bush administration’s detention policies and Liberal Fascism fans alike.)

Like most Mann films, Public Enemies requires a high tolerance for the cult of masculine cool. Dillinger was cool, fortunately, which means that Depp’s performance as the bank robber doesn’t require the suspension of disbelief that’s required to enjoy, say, Tom Cruise’s turn as a hitman-cum-existentialist in Collateral, or Daniel Day-Lewis’s playing Hawkeye as the coolest cat on the colonial frontier in Mann’s Last of the Mohicans. (It’s telling that Mann’s best movie, The Insider, came equipped with a protagonist — Jeffrey Wigand, a shlub of a tobacco executive — who was the antithesis of cool.)

This doesn’t mean that the casting is pitch-perfect. Depp has the right build, and a gymnast’s grace — Dillinger was nicknamed “Jackrabbit” for the way he leaped bank counters — but he looks more exotic than middle-American, and there’s an unfortunate echo of Captain Jack Sparrow when he slathers on the charm. (To really nail Dillinger, you’d probably want Depp’s charisma bottled into the body of William H. Macy.)

Bale is a more precise fit for Purvis: Stolidity roiled by moral anguish suits him, and so does playing the straight man to a more charismatic foil. Cotillard’s performance is a clinic in how to invest a predictably written part with real humanity. And the rest of the cast — the parade of cops, crooks, prostitutes, lawyers — is a nice round-up of vaguely familiar, immensely talented supporting actors from all over the Hollywood map.

Public Enemies is 20 minutes too long and unsatisfying at various moments, and Mann doesn’t really break any new ground along the way. But it’s exactly the kind of film that ought to benefit, come awards season, from the Academy’s recent decision to nominate ten films for Best Picture instead of five: a beautifully shot genre entertainment with some interesting social and political resonances. Is it great? No — but for what it is, it’s more than good enough.