According to the ads, the major selling point of Brooklyn's Finest is that it's from the director of Training Day. This is true! They are not lying about that. His name is Antoine Fuqua. He also directed Tears of the Sun, King Arthur, and Shooter, but never mind that. It's Training Day that Brooklyn's Finest most closely resembles, insofar as it's about rogue cops driven by personal agendas, and Ethan Hawke is involved.
What it also resembles, though, is a lot of other movies about rogue cops driven by personal agendas. Written by first-timer Michael C. Martin as an entry in a screenplay contest (here's a New York Times story about him), the film makes almost no effort to stand apart from its genre brethren, but it does benefit from solid casting and Fuqua's gritty, no-nonsense style. It even benefits a little from Ethan Hawke, which is somewhat rare these days.
Hawke plays Sal, one of three Brooklyn police officers who walk separate paths before converging later in the film. Sal, a plainclothes detective, has a family to support, including a wife (Lili Taylor) who's pregnant and in poor health. Sal has already reached the point of desperation when the movie starts, stealing money from drug busts and confessing to a priest, "I don't want God's forgiveness. I want his [expletive] help!" The priest is noncommittal on the subject of God's assistance in the commission of felonies.
Working out of the same precinct is Tango (Don Cheadle), currently deep under cover to infiltrate a drug ring run by a smooth crime boss named Caz (Wesley Snipes). Like Sal, Tango is desperate, but for different reasons: He wants to be promoted to detective, get out of the undercover line of fire, and sit behind a desk for a while. He wants to be a good cop, but this assignment is killing him. It's already ruined his marriage.