Dallas Morning News
You could get into a rousing debate over who gives the best performance, but the revelatory turn belongs to Mr. Damon. Some still choose to blithely dismiss him as an empty suit, but he's always had a rough-and-tumble, charismatic set of street smarts that leaps off the screen in the right role. This is the right role. He struts, he cracks wise, he sets his fellow cops up to die. His first encounter with Ms. Farmiga's shrink is a classic pickup scene full of humor and heat. More important, his clean-cut charm creates a dynamic friction between actor and role, the same kind of rich incongruity that allows Sullivan to con his police colleagues.
Even more of a revelation is Damon, who delivers a complicated, convincing and often surprisingly spontaneous performance as a politically ambitious cop. It doesn't hurt that South Boston and its tribal subtleties are things Damon knows well; when Sullivan looks longingly out of his apartment at the Massachusetts Statehouse, it's impossible not to see a slightly harder-edged version of Will Hunting behind the gaze.
Los Angeles Daily News
Damon is even better, turning Sullivan from a charming and skillful liar to a twitchy careerist consumed by self-preservation. Think of Damon's furtive work in "The Talented Mr. Ripley" and then take it one step further. This in an actor who digs deep and consistently amazes you.
New York Daily News
With young stars Leonardo DiCaprio and Matt Damon finally fulfilling their promise, and wily veteran Jack Nicholson adding another indelible character to his rich gallery, "The Departed" gets off to a ripping start and doesn't let up until its third or fourth twist ending.
Damon, who grew up in the Boston area and has the best accent, plays Sullivan as if being a dirty cop were the most honorable career a kid from the streets could have.
It won't happen, but these three guys deserve spots on the same Oscar ballot.
Damon's playing a more multi-leveled game, though, and under that mashed pretty-boy face we glimpse a whole spectrum of rat emotion: greed, ambition, cowardice, and a pathetic sort of loyalty.
Under Scorsese's direction, they meet the high-stakes challenge. Damon and Nicholson match up perfectly: The man without virtue, Sullivan, becomes the tool of Costello, the man without limits. Damon has a rare aptitude for expressing hollowness and the ache of hollowness, and the charm and wit a savvy guy can use to cover it up.
Salt Lake Tribune
In an ensemble of great actors (including Ray Winstone as Costello's right-hand thug), Damon and DiCaprio make a ferocious double act. They work off each other dynamically, even though they share few scenes together (Scorsese's intercutting is seamless, with all credit to his longtime editor, Thelma Schoonmaker). Both actors generate strong sparks with Farmiga, who should now be able to retire her title as the best American actress nobody's heard of.
The Damon/DiCaprio pairing is so powerful that Nicholson, for a change, has to break a sweat to steal the movie from them.
Oh, and then there’s Matt and Leo. Damon—in his first role as a bad guy since "School Ties"—nails the character’s cocky arrogance and, playing off his Bay State roots, delivers the best Bostonian accent in the film.
Matt Damon gives the best performance of his career as the creepy and conceited young wiseguy Colin Sullivan.
Damon, a consistently under-rated actor, makes full use of his coltish but brawny man-boy demeanour both to ingratiate himself with his department, and then to subvert it.
The same goes for DiCaprio and Damon, with the latter building nicely on his morally flawed roles in Syriana and the Bourne movies to deliver a stinging and tragic portrait of someone prepared to sell his soul for career advancement and an upper-class lifestyle.
Scorsese clearly trusts his actors, but the script provides much more embellishment. Damon is perfectly cast: He’s playing a variation of the lying manipulators in "The Talented Mr. Ripley" and (to a lesser degree) the "Bourne" pictures; for a leading man, he is amazingly adept at being slickly untrustworthy.
Salt Lake City Weekly
But even work as colorful as theirs can’t overshadow the magnificent performances of Damon and DiCaprio. Both seem destined to belong to the Paul Newman Club of actors so good looking that their talent might not be fully appreciated until they get their subscriptions to Modern Maturity. Yet they’re both in top form here as men so immersed in playing roles that they begin to lose a sense of who they really are. Nicholson gets to be his inimitably showy self—descending into paranoia and curling his eyebrows around speeches about rats—but The Departed belongs to his two young co-stars.