Shutter Island is an example of the genre they call a psychological thriller, as pretty accurately in Wikipedia:

• Psychological – Elements that are related to the mind or processes of the mind; they are mental rather than physical in nature. Sometimes the suspense comes from within one solitary character where characters must resolve conflicts with their own minds. Usually, this conflict is an effort to understand something that has happened to them. These conflicts are made more vivid with physical expressions of the conflict in the means of either physical manifestations, or physical torsions of the characters at play.
• Thriller – Generally, thrillers focus on plot over character, and thus emphasize intense, physical action over the character’s psyche. Psychological thrillers tend to reverse this formula to a certain degree, emphasizing the characters just as much as, if not more so than, the plot.
• Psychological thriller – Characters are no longer reliant on physical strength to overcome their brutish enemies (which is often the case in typical action-thrillers), but rather are reliant on their mental resources, whether it be by battling wits with a formidable opponent or by battling for equilibrium in the character’s own mind. The suspense created by psychological thrillers often comes from two or more characters preying upon one another’s minds, either by playing deceptive games with the other or by merely trying to demolish the other’s mental state.

This particular example was directed by no less a luminary than Martin Scorcese, who in turn has attracted a fine cast including Leonardo DiCaprio (far from being my favourite actor but commonly regarded as an A-lister), Sir Ben Kingsley, Max von Sydow, Michelle Williams, Mark Ruffalo among other competent and able actors.  

Here, much of the tale is relates to what goes on in the head of Teddy Daniels (DiCaprio) and which of the characters in this old-fashioned asylum, doctors, patients, warders and marshalls, is nuttier than the others.  There is a twist at the end, though I think it is fair to say that most people I know got the twist pretty early on.  Even so, critics were generally favourable in their response to Shutter Island.  Indeed the ending has even been the subject of academic debate, but since I won’t be revealing any more you can click here for spoilers!

To be fair, Scorcese has employed several clichés in order to ramp up the atmosphere, not least a craggy island packed with spooky buildings (serving perfectly as a mental institution for the criminally insane), a lighthouse and a cemetery, flashbacks encompassing nightmares, Nazis and a fatal fire, darkness, oh and a storm to end all storms, each of which element has on many occasions been used to keep cheap horror movies going even without the benefit of a sensible script.  You can’t blame Scorcese for that, though there is more than a sense of “been there, seen it all before” about Shutter Island.  A good director should be able to create ambience in any scenario, as Scorcese did with The Departed and Goodfellas, for example.

The slightly hackneyed retro nature of Shutter Island is further enhanced by the casting of DiCaprio, an actor specialising in a facial expression veering between a bewildered frown and an unsubtle belligerent and aggressive sneer, as if he is concentrating hard on something very distasteful just under his nose.  I’m not sure he is capable of any other expression, so deeply is the frown engrained into his features – exactly the same as his character in Inception, to name but one other movie.  It may only be my personal view but DiCaprio is regularly acted off the screen and can be rated on its merits in spite of his presence.

Actors with a greater range might have made more of Daniels here, but the movie is primarily plot-driven and Leo’s bafflement might just be caused by trying to figure out what is going on – though as I’ve said already, it’s not that difficult to see through the red herrings and work out what’s really going on here – the clues are there.  The story is eventually told in flashback.  Whether it’s remotely credible, psychiatrically speaking, is debatable, but then  it is a psychological thriller, and many of them have a tenuous hold on reality for dramatic purposes.

Bottom line is that Shutter Island is worth seeing, but I’ll tell you in advance that it won’t be the greatest thriller you ever saw.  Enjoy it for what it is but don’t expect profound revelations or the sort of meaningful philosophy hinted at in the flashbacks.  This is merely a competent thriller.