Johnny Depp plays Dillinger so straight, it's difficult to register how exceptional Dillinger was, even in scenes designed to highlight that very quality. The exception is the tension created when Dillinger strolls right into a police station, just as he did in real life. Christian Bale plays Melvin Purvis, the FBI agent assigned to bring down the notorious gang, and he's nicely buttoned up here. The scene in which he's forced to tell his boss J. Edgar that moral, clean, helpful young men are not going to get the job done is a nice juxtaposition of insecurity in telling the man what he doesn't want to hear, but with the courage of his convictions, as well as foreknowledge of what bringing in the gunslingers means for the community.
It's a Mann movie, so it's gorgeous, not the least reason for which is his reliance on closeups of Depp and the leading lady Cotillard. She plays Billie, the woman Dillinger woos with a fur coat nearly instantaneously. She is devoted to him, and he swears to protect her. Of course she would not need protecting if she were not John's girl.
There used to be a fantastic article about Mann's use of the extreme closeup, but that site seems to be gone now. Here's a quote by Mann, cribbed from a 3rd party, which gets at the point, I think.
I look for where or how to bring the audience into the moment, to reveal what somebody’s thinking and what they’re feeling, and where it feels like you’re inside the experience. Not looking at it, with an actor performing it, but have an actor live it, and you as audience, if I could bring the audience inside to experience.There are plenty of "that guy" actors, including David Wenham, Steven Dorff, Billy Crudup, and Jason Clarke, but I got a huge kick out of Channing Tatum as "Pretty Boy" Floyd. What a sport.
No big glamor, no big existential crisis-it is what it is. Dillinger robs banks. Purvis chases after him. People get shot, some die. Ultimately, Dillinger can not be taken alive, but the final confrontation is not even a confrontation so much as a shooting in front of a movie theater. It is what it is.