Johnny Depp has spent much of the past decade-plus playing fantasy characters ranging from Capt. Jack Sparrow to Willy Wonka and the Mad Hatter.

"Black Mass," in which Depp plays Boston gangster James "Whitey" Bulger, is being framed as his return to the real world. Don't believe it.

Bulger, as portrayed in Scott Cooper's film, is a hybrid of a lizard and a "wicked pissah" South Boston archetype. With his hollow eyes, balding dome and deadly quiet, menacing demeanor, the man feels like every bit of a fiction as Sparrow or Wonka.

Perhaps this is a sterling imitation of the real Bulger, who murdered a lot of people as he ran roughshod over the Boston crime world in the 1970s and '80s, and Depp certainly comes across as the sort of figure who might casually asphyxiate a teenager and immediately inform his lackeys that "dinner's in an hour."

It just plays a bit ridiculously, and certainly does no favors to a movie that must make us understand this terrifying figure, even a little bit, or risk seeming like little more than a pointless dirge through one killing after another.

Cooper appropriately bathes the film in dark shadows and grim compositions. The streetlights are dim, the interiors sparse and unwelcoming. This isn't Martin Scorsese's gangster universe, amped up in thrilling overdrive. The real Bulger recently wrote that he wasted his life, in a letter from prison to high school students, and "Black Mass" makes sure we understand that to the fullest possible extent.

The filmmaker gets closer to answering the critical question of "why," as in why tell this story at all, in the way he draws out Bulger's relationship with FBI Agent John Connolly (Joel Edgerton), a fellow Southie who protected Bulger as an "informant," but remained more loyal to his childhood friend than the interests of the bureau.

The most interesting parts of the movie don't involve Bulger at all, but the internecine politics at the FBI and the development of Connolly's steadfast betrayal of his professional and personal interests to enable the criminal. The bonds of friendship, forged out of the South Boston fire, remain tight and unflinching within this man, even when the sociopathic Bulger fails to reciprocate.

There's no understanding Connolly's motivations, and the Australian Edgerton seems to have more of a grasp on the accent than the character (the same goes for British Benedict Cumberbatch's work as Bulger's state senator brother Billy). So we're left with a movie about a bunch of people throwing their lives away for a violent maniac, out of fear or loyalty or whatever else. But that's hardly enough.