These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: The Departed
Acceptable Religious Targets: In the "Catholic priests are pedophiles" mold. One is mocked by Costello while another is mentioned as being a member of the Costigan family by Dignam early in the film.
Alternative Character Interpretation: Costello knows Costigan is a rat, but is too old and psychotic to care - and believes that, as he's an FBI informant and has Sullivan's help, he is untouchable anyway.
We briefly see Sullivan as an Altar Boy in the opening montage and hints about his sexual trouble as well as the frequent jokes about "Catholic priest as pedophiles" suggest that maybe he was molested as a child. In an interview with the French magazine, Positif, Scorsese implied that he was molested by Jack Nicholson as well. The character is in fact The Woobie who is trying to make it out of the ghetto, go to Harvard and become a good guy and overcome his childhood, which means he's as much of a Tragic Hero as Leonardo Di Caprio. Think of his final line to Jack Nicholson.
"Oh is that what you think this is about? All that fucking and no kids!"
Consolation Award: Despite its 93% Rotten Tomatoes rating and placing second of Scorsese's films on the IMDb Top 250 (actually Top 50; it ranks at #48), as well as being the highest ranked film of 2006, there are critics who believe the Academy Awards it received for Best Picture and Best Director were make-up calls for Scorsese's previous moredeservingwork having been snubbed at the Oscars. Oddly, it's rare to find a comment suggesting this that specifically advocates any of the other nominees (with the arguable exception of The Prestige, which failed to get a Best Picture nomination, though even that film's director, Christopher Nolan said that Scorsese would have been a deserving winner whether or not The Prestige was nominated).
One of the songs used in the movie was Badfinger's Baby Blue, but nobody really noticed. Fast forward seven years later, a certain TV show used the song for its finale, revitilazing the song in the progress
Narm Charm: Alec Baldwin is tremendously over the top in his usual way but is all the more funny and enjoyable because of it.
Also, Nicholson's performance. His unbelievable acting is completely hilarious, but it serves to make him so entertaining that the audience is forced to root for both him and the police.
Romantic Plot Tumor: There's really no reason for both male leads to hook up with the psychiatrist, other than to have some kissing in the movie. It's distractingly-pointless towards the movie as a whole.
Stylistic Suck: The ending with the obvious symbolism of the rat has provoked much criticism and head shaking. However, its likely that Scorsese, being The Movie Buff, is parodying the Executive Meddling endings of old gangster films where Karmic Death was enforced lest The Bad Guy Wins. The ending is a reference to the end of the film with All That Heaven Allows where a deer moves into the background frame for obvious symbolic effect, which the director of that film, Douglas Sirk admitted to the audience was him admitting to the audience not to take it seriously. The parody of the film in The Simpsons Lamphshaded the same.
"The rat symbolizes obviousness!"
Who's Your Daddy?: Very Subtle. It's noted during the film Sullivan is having dysfunction problems. However Madolyn and Billy spend a night together. She also walks past Sullivan at the end and indeed looks at him with contempt. Indeed upon finding out that Sullivan was a rat for the mafia, she tells him, "I thought I was the liar!"