While the film wallows in period detail and has some sporadic moments of amusing banter, it’s mostly flashy, empty and cacophonous, and it woefully wastes a strong cast led by Josh Brolin, Ryan Gosling and Emma Stone in barely developed, one-note roles.

At its center is a performance from Sean Penn as mob king Mickey Cohen in which he doesn’t just chew up the scenery, he rolls it around in his mouth like a handful of marbles, then spits it back out again and blows it to bits with a Tommy gun for good measure. With his mashed-up boxer’s mug, thick Brooklyn accent and volatile bursts of anger, he’s as cartoony as a Dick Tracy villain. While “Gangster Squad” certainly has its intended moments of humor, the laughs Penn’s performance prompts might not have been part of the plan. Or maybe they were — who knows?

The script from former Los Angeles police homicide detective Will Beall, based on the book “Gangster Squad” by ex-Los Angeles Times writer and editor Paul Lieberman, focuses on a time of flux in the city after World War II. Gang control of crime, cops and politicians had spread to the West Coast from places like New York and Chicago. Cohen had everyone of importance in his pocket and was on the verge of expanding his reach even further with a power play that would give him a piece of every wire bet placed in the Western half of the United States.

The gruff and grizzled police chief (a gruff and grizzled Nick Nolte) realizes the only way to conquer Cohen is to fight by his rules — that is, by no rules at all. So he asks Sgt. John O’Mara (Brolin), a principled, heroic war veteran, to put together a band of outsiders to destroy his empire without serving warrants or making arrests.

His sidekick is the initially reluctant Sgt. Jerry Wooters (Gosling, chain smoking and speaking in a weird, whispery voice), who prefers booze and women to trouble. Nevertheless, he makes the mistake of getting involved with Mickey’s moll, the classy, wannabe-star Grace. Stone is gorgeous with her wavy red locks, glam makeup and sexy gowns, but there’s not much to her besides looking good, which is a huge waste of Stone’s vibrant presence (not to mention the “Crazy Stupid Love” reunion she shares with Gosling).

The rest of the team consists of tried-and-true types, each of whom gets a one-liner here or there: the folksy, old-school gunslinger (Robert Patrick), the nerdy tech guru (Giovanni Ribisi) and — most dismayingly — the token black and Hispanic members, played by Anthony Mackie and Michael Pena, respectively. Seriously, that’s all they’re given to work with, and these are charismatic actors ordinarily capable of great command. (If you want to see Pena in a far superior movie about LA police officers, check out last year’s “End of Watch.”)

“Gangster Squad” was supposed to have come out last year, as well, featuring a climactic shootout in which gangsters fire automatic weapons from behind a movie screen at Hollywood’s historic Grauman’s Chinese Theatre. After the July shooting at a showing of “The Dark Knight Rises” that left 12 people dead in Aurora. Colo., that scene clearly had to be removed, which required extensive reshoots and a release-date change from September until now.

Still, you shouldn’t expect a kinder, gentler film. “Gangster Squad” is brutal, with a barrage of gunfire that becomes deafening and, ultimately, boring. The sheer volume of these gun battles, often depicted in stylized slo-mo or with quick blasts of light, undermines the significance of who’s going down and what’s at stake.

In the end, who lives and who dies doesn’t really matter. It’s all just noise disguised as entertainment.

“Gangster Squad,” a Warner Bros. Pictures release, is rated R for strong violence and language. Running time: 113 minutes. One and a half stars out of four.