Leonardo DiCaprio as the good cop.... Awesome. His best film since The Basketball Diaries.
Matt Damon as the bad cop....Eh. At first I didn't think his character showed enough depth, I mean, considering his role, he must have felt somewhat conflicted or guilty, but by the end of the movie, I hated him so much, that his performance became believable.
Jack Nicholson as the king of the Irish mafia.... awesome. I had heard that he was too theatrical, too "Jack being Jack," but considering he was playing Whitey Bulger, who by all accounts is a absolute monster, it's pretty much impossible to overdo anything. The portrayal of life in Southie under mob rule was accurate and hit a little too close to home for some people.
Mark Wahlberg as a detective....awesome. Brought so much authenticity to the film. I would put money down on him writing some of his own dialogue. For example, he calls DiCaprio "lace curtain," a term for snobbery I've only heard in Boston. When I moved from West Broadway to East Broadway, my former neighbors joked that I was becoming lace curtain Irish.
Martin Sheen as DiCaprio's police boss....Awesome, and somewhat presidential.
Alec Baldwin as the top cop....awesome.
Vera Farmiga as the police psychiatrist love interest of both Damon and DiCaprio...Liked the character, hated the TERRIBLE FUCKING FAKE BOSTON ACCENT. She sounded like an Italian from Long Island. Not quite as bad as Laura Linney in Mystic River, but still horrible.
Not everyone in Boston has a really thick accent. It's perfectly acceptable for some characters to lack an accent. No accent is much, much preferable than an awful fake one.
Everyone in Boston
So, only a couple of minor bones to pick with the plot. First of all, too much reliance on cell phones. Wouldn't the mob boss occasionally go through his people's recent calls? Wouldn't the cops look into phone records to see if they could determine who making the tip-off calls? Also, why did the police know everything about DiCaprio's past but didn't suspect Damon as the mole, even though he was also from Southie? Okay, enough nit-picking. Just go see it. Unless you're not a big fan of violence.