Woody Harrelson has come a long way since serving drinks in the bar where everybody knows your name. For his latest role as cop Dave Brown, he couldn't be further away from the good-natured barman Woody Boyd he played for eight years on the TV show Cheers.

It's 1999 and although the riots in Los Angeles are now seven years in the past, what happened then has not been forgotten. And it's understandable why, when cops like Dave Brown are still on the force.

Brown serves as an archaic relic of the bad old ways of policing. He behaves more like a corrupt sheriff of a wayward Western town rather than the more modern 'protect and serve' by the book kind of approach. His department gets that impression too.

He doesn't do himself any favours when he's caught on camera brandishing his own form of justice on someone who chose the wrong car to drive into: his. With the footage making the local news, Brown comes under scrutiny from the public and police officers alike.

With his peculiar family life also seemingly turning his back on him, Brown finds himself being forced into a tight corner – of his own doing – with no way of escape. But the fact of the matter is, Brown is the ultimate dirty cop, and he has no intention of cleaning up his act; instead, he just gets dirtier, whatever the consequences.

I know I've let myself go. You don't have to tell me that I don't look like the Deirdre you once fell in love with.

Harrelson's take on his character is deliciously dark. Brown has no redeemable qualities of any kind. He's a black hole with a badge, sucking in the light and life of those around him. Despite not being likeable in the slightest, it's difficult not to be fascinated by his antics. Harrelson really gets the grit of his character, as he gives quite possibly his best performance on film, which was sadly overlooked by the Academy this year.

But he's not the only one; the film boasts a truly impressive cast that includes Sigourney Weaver, Ned Beatty, Cynthia Nixon and Steve Buscemi. Two others who make slightly more of impression however are Robin Wright and Ben Foster; the pair, who play equally dysfunctional types, bring with them an uncomfortable rawness in their portrayals.

It's only the second film to be directed by Oren Moverman (the first being 2009's The Messenger), but his inexperience doesn't hold him back from getting not just under the skin, but deep within the polluted veins of both cop and city. It's no surprise to learn that he co-wrote the script with none other than James Ellroy (author of L.A. Confidential); so no wonder it's riddled with urban pessimism.

Rampart is essentially the West Coast version of the original Bad Lieutenant; it may well have slightly sunnier exteriors, but its dark core is just as disturbingly rotten.