Public Enemies takes awhile to get going, but once it does, it's a hell of a reminder why Michael Mann is one of the best directors working today. Almost certainly, he's the best at action—from the way Mann splits your eardrums with the sudden explosion of gunfire to how his handheld digital cinematography rushes you along in an exhilarating immediacy, watching the guy work when he's in the zone is pretty incomparable. 1995's Heat is always going to be his masterpiece, I think, but in moments and scenes in just about everything else he's directed—1992's The Last of the Mohicans, 2004's Collateral, 1999's The Insider, even 2006's Miami Vice—the guy's tossed off bits of cinema that'd be the high points of any other director's career. Mann can make desensitized audiences wince at the sight of a fist smashing into a face, yet he can also capture vistas and portraits with stunning grace and precision—and with Public Enemies, he gets the chance to do both.

But in order to get to that stuff, he has to wade through an uneven script, which he co-wrote alongside Ann Biderman and Ronan Bennett, based on Bryan Burrough's academically titled book Public Enemies: America's Greatest Crime Wave and the Birth of the FBI, 1933-34. Public Enemies follows bank robber/folk hero John Dillinger and FBI Agent Melvin Purvis; in the washed-out, worn-out years of the Great Depression, the ballsy Dillinger became something of a reality TV star before television existed, while the determined Purvis, under direct orders from J. Edgar Hoover, sought to bring Dillinger down. Here, Dillinger is a perfectly cast Johnny Depp, who brings his usual supplies of charm and intensity to his portrayal of the infamous criminal, while Purvis is Christian Bale, who has once again stapled his face into its now-familiar glower. They're great characters, and so is Dillinger's squeeze, Billie Frechette (Marion Cotillard), and so are the dozen or so peripheral characters who crowd Public Enemies' narrative, from Billy Crudup's officious J. Edgar Hoover to Stephen Graham's reckless Baby Face Nelson.

Public Enemies has a rocky go, trying to cram all of these messy, real-life cops and robbers into a Hollywood narrative: Obviously the real draw, thanks to the appeal of both Depp and the man he's playing, is Dillinger—but Purvis is important, too, even if he's not nearly as much fun to watch. Billie matters too, but not so much until the film's final act, so she kind of disappears for a chunk in the middle. As the film skips back and forth between Dillinger and Purvis, Mann lets his actors mumble, and he doesn't slow down for exposition—so as G-men and gangsters flit by, you're left to grasp what you can. Thankfully, that includes another killer performance by Depp, and more than a few rattlingly visceral Mann action sequences.

For all of Public Enemies' muddled attempts to delve into the history of America's first "war on crime," it works better as a thriller, an action flick, and a character sketch of Dillinger—and all of those are things which, in its fast-paced, sharply edited second half, Public Enemies becomes. "They ain't tough enough, smart enough, or fast enough," Dillinger says of the clueless but persistent flatfoots who're trying to chase him down—and after Mann's taken you along on one of Dillinger's bank robberies or jailbreaks, you can't help but feel the truth in what he says.