Shutter Island - Is it better to live like a monster, or die a good man?

Ominous score, the mysterious island and building sets, a long-suffering war-worn hero, suspiciously Nazi-like villains, the conspiratorial 50s, dark noir feel.

That last closing line - "Is it better to live like a monster, or die a good man?"

Its all a bit, but not quite perfect, Hitchcockian.

It is a good movie but I would not call it great. Somehow, somewhere, there is some sort of flaw.

Is it the interjection of nightmare sequences with the obviously fake blood? Is it the impossible rock-climbing athleticism of the protagonist, is the illogical expense undertaken to save one good man/monster? Is it the increasingly obvious conclusion we start arriving at mid-way through the movie?

Is it Leonardo? Or is it simple the thought that if someone else had played the main role, perhaps we would be faced with a more satisfy shattering end to the movie?