In the end, it all boils down to an easy bit of psychoanalysis, but until then, Martin Scorsese's Shutter Island walks a fine line between institutional thriller and what-is-reality? inquest, even as it never settles comfortably into either mode. As U.S. Marshal Teddy Daniels (Leonardo DiCaprio) makes his way to the eponymous isle, home to the Ashecliffe hospital for the criminally insane, he brings with him a hefty dose of psychological baggage. Accompanied by new partner Chuck Aule (Mark Ruffalo), Daniels arrives at the institution to investigate the disappearance of an inmate incarcerated for drowning her children. Soon, he begins suffering debilitating migraine headaches that trigger hallucinations involving a vague guilt that seems to derive from his participation in WWII (the film takes place in 1954) but is oddly conflated with images of the missing patient's dead children. When the woman suddenly returns to her cell and Daniels remains stranded on the island because of a hurricane, the Marshal begins uncovering what may be a grand plot involving mind control, ex-Nazis, and the HUAC—or which may be just a product of his fevered imagination.
Given the unwieldiness of the material, the project was probably doomed before Scorsese ever signed on, but while the director brings great attention to giving each scene a densely worked visual signature, his feel for the overall arc of the film is considerably less certain. Part of the pleasure Shutter Island offers comes from the self-conscious way Scorsese frames his leads against a gloriously artificial sky, the noir shadings he brings to the institution's cells, or a virtuoso tracking shot where he sends his camera rolling behind a line of Nazi guards being gunned down by U.S. soldiers. When Daniels's hallucinations, present in small measure from the beginning, start to take over the film in earnest, however, Scorsese begins to run into trouble, both because these dream sequences push beyond the handsome showiness of the rest of the picture into an unpalatable garishness, but more importantly because they throw off the balance of the movie.
No sooner is an initial level of reality established, the framework of a thriller set in place, then it's quickly undermined by this sudden shift into psychodrama. As a result, Shutter Island never gains the traction it needs to succeed as a suspenser and never sufficiently sets a bottom-line "reality" to ground an epistemological inquiry. Instead the muckraking thriller and the too-slippery psychodrama exist uncomfortably side by side, peppered with anachronistic political details and stretched out ad infinitum across endless scenes of clumsy exposition. As the film culminates in a recreation of the seminal event in Daniels's past, Scorsese seizes the moment to stage another impeccably crafted, visually precise set piece, even though the events that he depicts have just been described to us seconds before. This handsome bit of superfluousness proves that no matter how determined you may be to play each scene for maximal effect, there's a limit to how much significance you can wrest from your material.