* AdaptationDisplacement: Most people who went to watch the movie don't exactly realize it was based on a novel.
* AlternativeCharacterInterpretation: When Teddy recalls the liberation of Dachau and the mass execution of the guards, the film leaves it ambiguous if the Americans intended to kill the guards all along, or if it was an accident that became an unstoppable avalanche after one of the Americans guns down a guard who attempts to flee, causing the rest to panic and start firing on the remaining guards. Although Teddy's statement that it was murder may lead one to believe that the Americans had bad intentions for the guards all along.
* AwardSnub: Leonardo [=DiCaprio=] gives a heart-wrenching performance and wasn't even ''nominated'' by the Academy. He was nominated for Best Actor by six other awards associations. He didn't win any. Even after he won for ''Film/TheRevenant'', many still believe this is the film he should have won for.
* SugarWiki/AwesomeMusic: Even among those who didn't like the film, almost everybody has agreed that the soundtrack is very good. Of particular note is Max Richter's [[https://www.youtube.com/watch?v=rVN1B-tUpgs "On the Nature of Daylight"]], a beautiful piece which plays during Teddy's first dream about his wife and his encounter with George Noyce, as well as Music/GustavMahler's piano quartet during the WWII flashbacks and in the doctor's lounge. The film also uses music by Ligeti and Penderecki, which gained fame earlier in the soundtracks of films such as ''Film/TheExorcist'' and ''Film/TheShining''.
* HilariousInHindsight:
** Patricia Clarkson talking about a government testing project to create a dystopia. Fast forward to ''Film/{{The Maze Runner|Series}}'' films where ''she'' is the head of such a government.
** Mark Ruffalo as [[spoiler:the psychiatrist to a criminal with rage issues]] becomes positively hilarious once it's revealed - since Ruffalo is now known as The Incredible Hulk in the Franchise/MarvelCinematicUniverse.
** The subject of the plot is a young woman in a mental hospital who suffered SanitySlippage due to the death of a loved one and imagined an elaborate fantasy world for herself - and she's also played by a FakeAmerican actress with Emily as a first name. Are we talking about ''Shutter Island'' or ''Film/SuckerPunch''? [[spoiler:Both movies end with a character getting a lobotomy]].
** Twice more Leonardo Di Caprio would be haunted by visions of his dead wife - in ''{{Film/Inception}}'' and ''Film/TheRevenant''. The former (which came out the same year!) [[spoiler:has him responsible for the death after his wife went mad too]].
** [[Film/Titanic1997 Once]] [[Film/TheGreatGatsby2013 again]], Leonardo's character doesn't do well around water. Bonus points for all three movies being set in the past.
* MemeticMutation: Teddy's BigNO after [[spoiler:discovering his dead children]] became used in memes after a while.
* MoralEventHorizon: Dr. Naehring arguing in favor of leaving the patients shackled to the floor to potentially drown. [[spoiler:Quite probably an intentional KickTheDog moment to solidify his image as a mad Nazi doctor in [[strike: Teddy's]] Andrew's imagination.]]
* {{Narm}}:
** The [[https://www.youtube.com/watch?v=ebeiX7HIsw8 opening theme]] can be a little over the top, especially when all that's happening is a boat approaching an island. Oh no... waves! DUN DUN DUN!!!! And then it arguably turns into full-blown NightmareFuel when [[spoiler:it plays over the shot of the lighthouse at the very end of the film]].
** "Marshall...you have no friends." Intended as a way of saying "Trust no one", but it sounds remarkably like a childish insult.
** A likely intentional example here: When Teddy and Chuck enter Ward C, the atmosphere is quiet and intense, a look of solemn determination across Teddy's face. All of a sudden, [[https://www.youtube.com/watch?v=3izfCoGAlRo "Tag! You're it!"]]
** Teddy's line about Andrew Laeddis "he lit the match that started the fire that killed my wife" - quite an awkward mouthful.
** Dolores's name is never spoken on screen until the scene where it's revealed to be significant - [[spoiler:an anagram of Rachel Solando]] - making it feel less like the WhamLine it's meant as.
** Teddy[[spoiler:/Andrew Laeddis]] suddenly fainting in the lighthouse after being overwhelmed with realizations should be serious and solemn, but the sloppy way he faints to the floor and Dr Cawley and Chuck's scrambling to pick him up is perhaps a bit too comical compared to the otherwise tense and deep emotional weight of the scene to take seriously. The fast camera zoom out doesn't exactly help it either!
* OlderThanTheyThink: The book has been unceasingly compared to Torcuato Luca de Tena's ''Los renglones torcidos de Dios'', a 1979 Spanish novel with a very similar plot and feel (metalheads might have heard about it because it inspired an eponymous song by Music/MagoDeOz in what is considered their best album ever in 2000). Amusingly, when this novel received its own adaptation in 2022, its director Oriol Paulo revealed he was influenced in turn by the ''Shutter Island'' film.
* OneSceneWonder:
** The inmates interrogated by Teddy give one hell of a performance, particularly Creator/JackieEarleHaley.
** In the one scene in which he has any dialogue, Creator/TedLevine delivers a gripping CharacterFilibuster on how violence is a gift from God [[spoiler:(which arguably doubles as some variant of TheReasonYouSuckSpeech to Teddy/Andrew about what the warden sees as the inevitability of his lobotomization).]].
** Patricia Clarkson as the [[spoiler:imagined]] Rachel, who Teddy finds camped on the island. She doesn't appear past this scene, but provides plenty of Nightmare and Paranoia Fuel (see below).
* ParanoiaFuel:
** [[spoiler:The imagined]] Rachel says that in fifty years, the Ghost project will be operational. The book takes place in 1954. It was published in 2003. [[spoiler:Subverted. There is no Ghost project.]] That we know of anyway.
** The reveal is sure to make you think "What if I'm [[spoiler:actually crazy, and my life is a just an insane asylum's role-play game to bring me back to sanity?]]" and that you too could be a [[spoiler:dangerous killer]] and not have the slightest clue about it.
* TheUnTwist: Any viewer should be able to spot the obvious twist a mile away, but the way the film plays out makes one constantly question whether or not that's just what the filmmakers want you to expect.
* TheWoobie:
** George Noyce, a once promising graduate student who became psychotically violent and is destined to spend the rest of his life in a mental hospital (and probably get lobotomized). During his lucid moments, George tries to help Teddy [[spoiler:accept reality and avoid the same fate,]] and is almost beaten to death for it (which doesn't stop him from continuing to try to help Teddy).
** Teddy probably qualifies as well, especially during his breakdown when [[spoiler:the truth about "Laeddis" is revealed, and in the final scene where he hints that he's basically faking insanity to allow himself to be lobotomized.]] While he had his character flaws (he drank to avoid having to deal with [[spoiler:his wife's mental illness]] and his traumatic experiences of WWII), everything in the film indicates that he was otherwise a basically decent man whose life and sanity were destroyed by a personal tragedy.
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