A good movie, but not as good as the Chinese original, Infernal Affairs. The main strength of this movie is the concept and plot, taken pretty much straight from the original, and still as compelling. Where The Departed suffers in comparison is in some of the actors. Maybe it's just because the American actors are more familiar to me than their Chinese counterparts, but here in particular Nicholson and Baldwin stuck out as sore thumbs. Scorsese apparently decided to let them run wild out of control, and Nicholson in particular just became tiresome as he went on. Not as bad as, say, Brando in The Score, but so noticable as to pull me out of the movie. I'm not sure why all of the players outside of DiCaprio, Damon and Vera Farmiga (and Farmiga ended up with the opposite problem, underplayed relative to everyone else) were played so broadly here, but it was a bad decision.
Still, the plot is strong enough to overcome much of that, so four stars.