Probably the best directed B movie I've ever seen.
The first two acts of Shutter Island are probably the best movie I've seen so far this year. The only problem is that the third act is so ridiculous and unambiguous that it brings down the whole enterprise. I don't want to ruin it for people who have yet to see the movie, but the ending retroactively ruins a fair amount of very effective and suspenseful scenes. Think The Usual Suspects but with a better first two acts and an even sillier and less plausible ending.
Even with the silly ending, this still worth seeing. The acting and directing is, as expected, all top-notch. I probably expected too much from the screenplay, but before being derailed at the end, it is very immersive and interesting. The influence of classic Hitchcockian thrillers is most evident in the score and cinematography. Unfortunately, even with all these outstanding elements, the plotting causes the film to fall far short of the classic it would have been otherwise.