Shutter Island was a solid thriller for my money. I did like it, but it was pretty heavy-handed. You had the blaring "YOU ARE ENTERING DOOM" music the first note, and DiCaprio staring off into the horizon like a damn pirate right away. It lays it on thick.
The effect is that the 'twist' is fairly predictable, and I had mentioned it to my girlfriend about the time he starts wandering to the rocks. Her reaction: "I hope it's better than that." Then the last shot is a bit gimmicky: well, was he right in some way? Ohhh, boooyy. It was a notch below the Goosebumps books I would read as a lad. When the hand would pop out from the grave, or the new "doll" that replaced the evil one suddenly blinked and smiled on the shelf.
But I don't think the point is that Scorcese is trying to do anything all that new here. We know Scorsese is a film historian, and as noted by critics, this is more of his paying respect to the greats in his art (though in much more of a subtle way than the fanboy Tarantino), like Hitchcock and Robert Wise.
For me, the best part of it was the post-War atmosphere. The scare of atomic bombs, flashbacks to the obviously traumatic events of being a soldier, HUAC conspiracies, Nazi conspiracies, etc. The setting really made the movie. And with that, Scorsese throws us into eerie dreams and impacting flashbacks, and it's a good process that worked for me.