RUBEN Fleischer, famous for his wisecracking comedies Zombieland and 30 Minutes or Less, has now made his career step up to a bigger, meatier picture.

Gangster Squad is an all-star action thriller based on a true story and set in 1940s Los Angeles, all about a secret crew of incorruptible cops taking on a Brooklyn mobster, the sadistic and creepy Mickey Cohen. Mickey is hammily played by Sean Penn under heavy prosthetics, behind which those unmistakable hooded eyes glower from further back than usual. The movie is slick but shallow, pretty watchable, very violent.

It’s not quite in the cynical tradition of James Ellroy: the emphasis is on the good guys in uniform. Chief among them is lantern-jawed Sergeant John O’Mara (Josh Brolin) whose pregnant wife is at first worried about her man’s dangerous work, but then turns sassily on a dime and starts enthusiastically helping to pick out squad recruits. One of these is Jerry Wooters (Ryan Gosling) who is having an affair with Cohen’s girlfriend Grace (Emma Stone).

The LA period detail is intricate and the dialogue exotic. When absenting herself to the bar while the men talk business, Grace says: "I think I’ll bend my elbow while you guys bend your ears!” For all the guns and gore, it’s as breezy and uncritical as a tale from the True Detective magazine that the cops can’t help reading.