Gangster Squad, the new film from Zombieland director Ruben Fleischer, got some undue attention this summer when it hastily moved off its original September release date and was pushed to January. The reasoning was that the movie contained a scene in which gangsters opened fire in a crowded movie theater, not exactly a welcome image in the wake of the Aurora shootings. So they went back to work and filmed a new scene (now set in Chinatown) and now this week, at long last, is the arrival of the much-delayed film. It really wasn't worth all the fuss.

The film, set in 1949, tells the tale of dogged, loose-cannon police detectives busting the operation of notorious East Coast-transplant gangster Mickey Cohen, the former pugilist turned crook who had connections with the Mafias both Jewish and Italian, and beyond. Cohen has, the movie insists, taken over Los Angeles, turning it into a sleazy hotbed of crime instead of the, what, slightly less sleazy lukewarm-bed of crime that it used to be? This is Los Angeles we're talking about, isn't it? Well, whatever, it's not really important, as this movie is not chiefly concerned with historicity. No, the name of the game here is guns 'n' gristle, with two craggy-faced foes squaring off against one another at the expense of mucho collateral damage. Josh Brolin plays Sgt. John O'Mara, a Camp X-trained WWII hero who approaches his police work with the blunt swagger of a lone vigilante. He's rough and taciturn, except of course when it comes to his pretty, pregnantly glowing wife (Mireille Enos), who gives wise counsel and gently bathes her brutish husband after a tough day of crackin' skulls. Sean Penn, looking small and wolverine-ish here, plays Cohen with a furiousness that doesn't suit the rest of this cartoon-y movie. Were Brolin and Penn playing these warring galoots in some other, darker, smarter movie, we could have something interesting. But as is, it's a lot of glowering for only a little payoff.

Fleischer, as he proved in Zombieland, is a mainstream filmmaker with elan — the first half of Gangster Squad tingles with wit and primary color pizzazz. In particular, there's a long, smooth nightclub scene where the film's two love birds — ne'er-do-well cop Jerry Wooters (Ryan Gosling) and Cohen's slinky "etiquette teacher" Grace Faraday (Emma Stone) — have their cigarette-sucking first encounter. The scene is awash in cool metallic blues and reds and pops with a wry smile. Fleischer seems to relish in all the old noir-ish cliches of the genre; the rake with the heart of gold, the tough but imperiled dame. The actors dance nimbly through scriptwriter Will Beall's more rat-a-tat-tat passages, and everyone, on camera and off, seems to be having a ball. If only Fleischer could have maintained this energy, made a slightly arch and self-aware gangster flick that was mostly charged conversation, rather than quickly stooping to make the junky action picture the film turns into about halfway through.

O'Mara is tapped by Nick Nolte's gravel-throated chief of police to put together the titular gangster squad, a task O'Mara hands over to his knowing wifey. She sets him up with your usual ragtag group. There's Robert Patrick as the grizzled old six-shootin' cowboy cop. Anthony Mackie plays a quick-with-a-knife funny guy from Central Avenue. Giovanni Ribisi, always a welcome sight, is the nerdy, earnest tech guy with a family at home. And Michael Peña plays a tag-along novice who's endearing as he is green. They're all types we've seen before, and the film has some fun playing them up. But eventually Fleishcer and co. have to move on with their actual movie, and that's where things go south. The guys set out to destroy Mickey's various operations one-by-one, but what they really end up wrecking is the movie they're in. As the violence mounts, the rest of the film's tissue dries up and blows away.

Wooters and Grace's romance, for example, is a cursory seduction at best. They get their meet-cute, their bedroom scene, their sensitive scene, and that's about it. Stone is underused in other ways, too. Though Grace is supposed to be Mickey's gal, a relationship that has some actual consequences later in the film, Penn and Stone are barely seen together. Which speaks to a larger problem in the film. Much of what initially looks rich and textured reveals itself to be merely a studio lot flat, and is eventually carted off to make room for sprays of Tommy gun bullets; action that's done with as much clatter and scramble as any second-rate action movie these days. Fleischer seems to think these set pieces are where he excels, but he's wrong. It's in the glossy beginnings, in the ring-a-ding tweaks of a beloved old genre where he's doing good work.

But, alas, Fleischer listens to his action instincts, and pretty soon we're getting Penn barking "Here comes Santy Claus!" as he unloads in a hotel lobby (that line does, admittedly, play kinda well) and slo-mo shots of bullets piercing Christmas ornaments and other decorations. Once the film gets going in these stretches, and tries to go for some real grit and seriousness, all the corny dialogue and composition seems less like a sly joke and more like the signs of a clunky script. There was hooting, definite hooting, at my screening by the time the movie ended, and it was directed at the scenes that were going for sincerity. Fleischer has made a jumble of a film here, one that begins strongly and features fine actors gliding around with period ease, but too quickly becomes just another dull action picture. Why is everyone in costume, I found myself wondering. What's the point of all this detail and research? Ultimately this gangster squad could be doing its grim work in any place, in any time. By picture's end it's all rather weightless and arbitrary, everyone standing there in silly sagging suits with prop guns in their hands. There are definitely moments when the film sings — Gosling struts, collar up and hat down, into a police station; a violent raid is intercut with a jazzy nightclub performance; Emma Stone stuns in a long blood-red gown. But the rest of it feels like clutter. I wonder if it's too late to do some more reshoots.