Impressions before seeing it
The trailers really built it up as a mindblowing mystery, plus with a good cast and director backing it I knew it was going to be good.
How was it?
Shutter Island starts out like a classic mystery (trenchcoats, fedoras and all) and then, taking place in an island-locked mental institution, progressively gets more muddled and confusing. This isn't a bad thing, as everything makes sense by the end; in fact it makes the experience more enjoyable because I went through several different theories about what was going on, and then changed them each time a character offered a new explanation or piece of evidence. I won't spoil the ending here but I will say that one of my guesses was correct... partly, anyway.
As with anything involving a twist ending, Shutter Island can be appreciated in subsequent viewings because you can look for the hints and have a better understanding of what's going on. I've only watched it once, but just thinking back to certain moments makes the ending even better. I will admit, though, that the reveal didn't exactly blow my mind. While it wasn't necessarily expected, I was just sort of like "Oh, okay, that's what's going on. Makes sense." Maybe it was the manner in which it was executed: people standing around and calmly explaining it. I suppose it was necessary, but it almost felt anti-climactic.
Recommendation
I think I was just a tad disappointed, but I don't want this to sound like a negative review. It is a very smart and well made mystery that keeps you guessing (a lot), and I'm glad I watched it. You probably will be too.
