“Cops or criminals ... when you’re facing a loaded gun, what’s the difference?”

That’s the amoral attitude of Frank Costello (Jack Nicholson), a ruthless Irish mob boss who runs south Boston with a bloody fist.

Young Colin Sullivan (Matt Damon) agrees with him. And since he’s looked up to Costello as a surrogate father for most of his life, Colin would rather be on the criminal side of the divide. But Billy Costigan (Leonardo DiCaprio) sees the choice as less about power and more about right and wrong. He’d rather be a cop.

They’re the central characters in “The Departed,” a violent, deeply engrossing drama that marks Martin Scorsese’s returns to the mean streets of crime. And in it, the director and writer William Monahan achieve an almost-Shakespearian level with their tale of betrayal, treachery and murder.

Though “GoodFellas” may come to mind, the milieu this time is Boston Irish instead of New York Italian. And yet, the filmmaker seems so at home, you’d swear he was an O’Shaughnessy instead of a Scorsese.

“The Departed” is very loosely based on “Infernal Affairs,” a recent Hong Kong thriller; yet it has a feeling of intense originality and homegrown realism.

“The Departed” focuses on a special crime unit, established to bring down the town’s leading gangster and his mob. It’s a mirror-image story of double jeopardy, with Costello’s man, Sullivan, becoming a cop to inform his mob boss about police activities, and cop Costigan going undercover in the mob to inform the police of Costello’s plans.

They work at cross purposes and send both sides of the equation into all sorts of compromised situations.

Opposing Costello and his gang are the top cops — played by Martin Sheen, Alec Baldwin and Mark Wahlberg — three actors who deliver fine character performances, obviously relishing the opportunity to work for one of the greatest directors on the planet. And at Costello’s right hand is “Mr. French,” a violent thug without an ounce of conscience (who’s played by the brilliant British actor Ray Winstone of “Sexy Beast” fame.)

And serving as a referee, of sorts, is a police psychologist (Vera Farmiga), who occasionally provides the sort of insight Tony Soprano gets from his shrink. She’s also an intriguing love interest that adds even more to the competition between Costigan and Sullivan.

“The Departed” is riveting, in-your-face entertainment, with a visceral energy, intelligence, dark wit and several first-rate actors doing their best work ever. Working with his frequent cinematographer Michael Ballhaus, Scorsese has come up with a nearly perfect, quick-cutting visual style. (You always see something new in a Scorsese film; here’s it’s the infinitesimally quick, almost unnoticeable freeze frames that underscore each death in a shootout.)

Martin Scorsese never makes a bad movie; he just makes some that aren’t quite as artful or meaningful as others. No worries here, this is among his very greatest films.

Rated R, with very strong violence, profanity, drugs and sex. Four stars out of four.

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Jessica Simpson, Dane Cook, Dax Shepard and colleagues will not be in the running for Hollywood’s employee of the month for their new comedy "Employee of the Month."

Except for standup comic Cook, who manages to come off as likable enough in this dreadful workplace tale, everyone else involved belongs in the unemployment line.

First-time director Greg Coolidge shares screenwriting credit with Don Calame and Chris Conroy, and it’s a sorry day on the job when it takes the toil of three people to come up with a comedy so lame and gags so pathetic.

Set at a bargain warehouse store, the movie pits Cook as a slacker box-boy against Shepard as an odious super-drone competing for the latest employee of the month contest, both convinced that winning is the only way to win the heart of a gorgeous new cashier (Simpson). Simpson is so flat and vacuous, she delivers her lines with all the personality of a 10-pound can of cling peaches.

PG-13 for crude and sexual humor, and language. 108 min. One and a half stars out of four.