“Public Enemies” makes a rather strange midsummer release. This somber gangster piece set in the 1930s comes out at a time when transforming robots and Sacha Baron Cohen’s latest affront to comedic taste (“Bruno”) look sure to rule the box office for weeks.

With his latest crime drama, director Michael Mann (“Heat,” “Collateral”) clearly aims to attract both the adult audiences who want a smart, fresh telling of the John Dillinger story (with which we are already familiar) as well as the 17- to 24-year-olds who make up most of the summer box office. What Mann proves, though, is that it’s tough for one movie to satisfy both groups.

“Public Enemies” depicts the ’30s as a time when bank robbers ran amok, the young Federal Bureau of Investigation struggled to figure out how to stop them and the innocent victims of the Depression are caught in the crossfire of this deadly cat-and-mouse game.

The film attempts to cover a lot of ground. It focuses equal attention on John Dillinger (Johnny Depp), his love affair with Billy Frechette (Marion Cotillard) and the quest by J. Edgar Hoover (Billy Crudup) and Melvin Purvis (Christian Bale) to track down not only Dillinger but also Pretty Boy Floyd (Channing Tatum), Baby Face Nelson (Stephen Graham) and Alvin Karpis (Giovanni Ribisi) — not to mention the scores of men who work with them.

We alternate between Purvis’ attempts to track the criminals and the lives and times of the criminals themselves. We get to see the story from both sides, a bit like “Heat” meets “Bonnie & Clyde.”

Mann and his writers ambitiously shoot for a sprawling crime epic, but they have spread themselves too thin. We get a decent surface treatment of many characters but we only become fully acquainted with Dillinger and Frechette. Even with those two lovebirds, though, we’re never shown what motivates them to live their notorious lifestyles.

Mann does his best to build a tragedy around his characters, but it fails to arouse much sympathy simply because we don’t know them very well.

So why try to cover so much ground? Why not tell the story of just Dillinger, his gang and the love of his life? Or dramatize the story of the burgeoning FBI in more detail?

All valid questions, because “Public Enemies” runs about 30 minutes too long and neither lifts us to swelling heights nor moves us to tragic tears. The ending in particular feels dragged out and forced, as if Mann knows we haven’t yet fallen in love with the movie and this is his last, desperate attempt to woo us.

Still, this is Depp, Cotillard, Bale and Crudup supported by an excellent cast. So of all the mediocre movies we’ll see this year, this might be the best. Which means while it isn’t great, this talent pool gives the film a huge boost.

Mann and company do deserve credit for refusing to fully glamorize characters who have often been depicted as romantic robber barons. Sure, “Public Enemies” occasionally makes the lifestyle Dillinger and his cohorts lead look swell, but as soon as they stop to pop the Champagne and smell the roses, the police crash the party.

The film repeatedly reminds us of the brutality and brevity of this life. The crack of police batons on bones and the awful slamming of prison cell doors burst into our ears. Dillinger’s friends, one by one, die violent and pointless deaths. Crime pays for a while, then it’s time to pay it back.

“Public Enemies” is the sort of film we like but wish were a little better. Still, Mann has created an enjoyable crime drama that offers grown-ups an alternative to robots and the second coming of Borat. And we thank him for that.

Jeff Marker is a media studies professor at Gainesville State College.