Michael Mann’s latest feature has a reported budget of $80 million (£48 million). In Johnny Depp it boasts one of the most bankable stars currently working. And yet it has the production values of a bargain-basement, made-for-television flick. Something here just doesn’t add up.

Mann, like several of his contemporaries, most notably Steven Soderbergh, has enthusiastically embraced digital technology. But rather than try to recreate the look of 35mm film using the cheaper and more versatile digital alternative, Mann’s aim appears to be to develop a new, distinctive digital aesthetic. Which is admirable in theory, but Mann’s digital aesthetic seems to involve making the movie look as grimy and unpolished as possible. Post-production is for wimps. That irresistibly glossy, larger-than-life reality created by Hollywood movies is diminished here. The flat glare of the digital camera emphasises the artifice of the film-making process rather than bringing the hoped-for gritty authenticity to the story.

It’s not just the look of the film that suffers at the hands of Mann and his defiant lack of refinement. The sound mix is chaotic. It sounds as if the words are blurred. Key lines of dialogue are lost to random swells from the score, others jump in volume for no apparent reason halfway through. It’s so messy that I rang the distributors to check whether there was a technical problem with the print they showed or the cinema they screened it in, but both were apparently fine.

Questionable production values alone are not enough to sink a movie. Cinema doesn’t have to look great if it has something to say. But it’s not entirely clear what Public Enemies is trying to say. It’s a sprawling period piece that blends a lot of fact and a bit of fantasy in the telling of the story of John Dillinger, the Depression-era bank-robber and, for some at least, a Robin Hood-style popular hero.

Depp takes the central role but, even with his undeniable skill and charisma, fails to invest the role with much detail other than the fact that he’s a bloke who robbed banks and had a taste for dandyish clothing. Slightly more interesting is Billy Crudup’s meticulously prissy portrayal of the young J. Edgar Hoover, then the head of the fledgeling FBI and already an accomplished manipulator of headlines. Slightly wasted is Christian Bale as Melvin Purvis, the agent in charge of bringing Dillinger to justice. The way the film tells it, Purvis is motivated by nothing other than pursuing and gunning down miscreants.

If the film had focused on these three men and the battle of wits between them there might at least have been room to develop them as characters. Instead, Mann crams the movie with peripheral historical presences. Pretty Boy Floyd (Channing Tatum) turns up just long enough to get splattered by the righteous bullets of the FBI. Baby Face Nelson (the British actor Stephen Graham) features in a nice little scene in which he convinces a pair of agents that he’s a shoe seller by trade, but then disappears into the background for most of the rest of the film.

Certainly the action set pieces are ruthlessly, gorily efficient, as you would expect from a director of Mann’s skill and reputation. But without the character depth to make you care whose blood is getting spilled, you might as well be watching a movie by Michael Bay.

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