This movie is actually a remake of Hong Kong's Mega-blockbuster movie - The Infernal Affairs, that's have an unique storyline about cat-and-mouse game can be articularly played when cops and gangsters are always loyal rivals and only witted ones will always the last to stay. This movie has good cast that features well known actors (even in the HK ver) and director.
Here are the cast as shown below:
Leonardo deCaprio plays Tony Leung's character as a undercover cop who's assigned to infiltrate and nail the mob syndicate run by gangland chief. No comments.
Matt Damon plays Andy Lau's character as an informer for the syndicate who run by a gangland chief. Both (Matt & Andy are able to sing - Matt has a jazzy voice as he sings 'My Funny Valentine' in the movie 'Talented Mr. Ripley', while Andy is a HK canton-pop singer. Well, it's nothin' to do with the cast).
Jack Nicholson plays Eric Tsang's character as the gangland chief who is a ruthless mob who run the syndicate with his unlawful ways. Most wanted person by the Special Investigation Unit police force. He's too tall for this character but his cunning and wicked-grining face works in this play.
Probably Martin Sheen plays Anthony Wong's character as Tony Leung's friend & superior that in charge of the Special Investigation Unit Force. He's too old to fit in Anthony's shoes as a workalcholic and complex-looking cop.
For your information, this movie is directed by Martin Scorsese - who has directed the movie 'The Aviator'.
This trailer is indeed less intriguing as the original HK Internal Affairs trailer has more impact on delving one's character with emotions and charisma. The difference is that there are some kissing and bed scenes in this hollywood movie. Hope that this movie looks good when it's on screens. Watch this clip below - The original always does good (The Infernal Affairs).
Favourite quote from the movie 'Infernal Affairs':
"I'm sorry, I'm a cop" spoken by Tony Leung's character as a undercover cop when he's pointing a gun at the back of a cop - who's an informer for the syndicate.