“Black Mass,” the movie all of Boston has been dying to see — shot right here in our own back yard, where these grizzly events unfolded — is a funereal event. It’s a solid film, with an impressive central performance by Johnny Depp as Boston crime lord James “Whitey” Bulger, but it never rises to the level of greatness like “The Godfather” or even “Goodfellas.” A too-lean screenplay and the lack of a compelling, cohesive vision by director Scott Cooper deadens some of the drama. Though the performances are good-to-great, the tale onscreen seems smaller and less powerful than the actual events warrant. The screenplay fails to flesh out its secondary characters, and the direction doesn’t give enough dramatic weight to this tangled web of corruption and its resonance in our city.

Based on the book “Black Mass: The True Story of an Unholy Alliance Between the FBI and the Irish Mob” by Boston Globe reporters Dick Lehr and Gerard O’Neill, the film does do a good job of delivering the facts about the incestuous relationship between the FBI and Whitey Bulger. That relationship quashed one group of criminals, the Italian mob, but allowed another criminal empire, run by the Irish mob, to flourish.

The film begins in 1975 and ends in 1995 with Bulger’s disappearance and eventual emergence at the top of the FBI’s 10 Most Wanted list. Seen in flashback, members of Whitey’s Winter Hill Gang — Steve “the Rifleman” Flemmi (Rory Cochrane), Kevin Weeks (Jesse Plemons), and hit man John Martorano (W. Earl Brown) — dispassionately recount their horrifying stories of murder and intimidation in exchange for immunity or reduced sentences.

The film zeros in on Whitey’s rise to power. He was already a criminal, had spent time in Alcatraz, and was a “small town player” on the ascent in South Boston when he was approached John Connolly (Joel Edgerton), a childhood friend who’d become an FBI man. The deal is very clearly spelled out: Connolly proposes an alliance with Whitey to inform for the FBI on their mutual enemy, Boston’s Italian mafia under the Angiulo family, in exchange for leaving Whitey and his Winter Hill gang alone… as long as they didn’t kill anyone. Right. In effect, the FBI fought Whitey’s battles for him against his Italian rivals, while he grew more powerful and ran roughshod over the city. This was all in exchange for information that it seems the FBI could have gotten itself, or which wasn’t all that crucial anyway.

The bare and bloody facts are laid out, with no detail spared. Within the first 10 minutes Whitey beats someone to a pulp in broad daylight. The gruesome murders unfold with regularity, and the proceedings unravel like a list. Which brings me to Depp’s performance, on which this undernourished screenplay depends.  This is one of the great Johnny Depp performances in a career full of them, and I’m not talking about the  “Pirates of the Carribean” franchise, but rather his nuanced turn in “Donnie Brasco” in which he plays an FBI man who goes undercover as an informant and discovers he has more in common with the criminals than with the FBI.

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As Brasco, Depp was clearly Depp — the handsome, almost pretty leading man, seen as complex hero. As Whitey, he’s almost unrecognizable. Physically he’s an even more evil version of the mysterious gangster we’ve seen in pictures, compact and coiled, ready to spring anytime, anywhere. Depp’s performance seems to take at least part of its cue from the film title itself, not only a reference to “MASSachusetts” during Whitey’s dark reign, but also a reference to either a Satanic mass or a traditional Catholic requiem mass for the dead. Depp plays Whitey like a vampire, with icy blue eyes, rotten teeth, pale skin, and slicked back hair over a face like a skull. In many scenes, often before he kills, he is deathly still, then suddenly white hot. Remarkably, in other scenes he appears intensely and warmly devoted to his young son. That Depp synthesizes these disparate qualities within a single coherent character is no small feat.

As John Connolly, Joel Edgerton (whom we recently saw as the creepy weirdo in this summer’s thriller “The Gift”) is again thoroughly convincing. Ditching his native Australian twang for a subtle Boston accent, he renders Connolly as a guy playing all the angles, who knows where his bread is buttered but is ultimately loyal to his Southey roots. He gradually morphs, scene by scene, into the gangsters with whom he once ran the streets.

But beyond these two pivotal roles, the other actors are either wasted or made to seem superfluous in underdeveloped parts. Would that director Scott Cooper (“Crazy Heart”) and the screenwriters had provided a meatier script for Depp to sink his teeth into. The excellent Sienna Miller, who was to have played Whitey’s girlfriend Katherine Greig, was cut entirely from the film. Benedict Cumberbatch is miscast physically as Massachusetts Senate President William Bulger, Whitey’s brother. . Not enough is made of their ambiguous relationship; what we are given to understand, in every scene, is only that Billy didn’t technically let himself know what he shouldn’t know.

Medford Mass native Julianne Nicholson (“Masters of Sex,” “August: Osage County”) is perfect as Connolly’s supportive (then resentful) wife Marianne, who has a terrifying encounter with Whitey in her home one night. But this scene runs long and should have been truncated to preserve its power. Dakota Johnson (“Fifty Shades of Grey”) is surprisingly affecting as Lindsey Cyr, the mother of Whitey’s son. Kevin Bacon is wasted in an underwritten part as Connolly’s superior at the FBI, but at least his Boston accent has simmered down since “Mystic River.”

At other times the film is downright derivative. There’s a moment  of a shadowy Depp looking down from on high inside a church; later, there’s a great shot of him seen from above, laid out coffin-like on a settee. But the director never takes these images and runs with them, or exploits their thematic implications so they resonate. Another scene, clearly ripped off from a scene with Joe Pesci in “Goodfellas,” has Depp’s character toying with an FBI man over a family recipe. We know exactly where this is going, and so the life goes out of the encounter long before it plays out.

For Bostonians, there’s lots to recognize — shots of street corners in Dorchester and Quincy, and the stony grey building in Government Center where the FBI is ensconced. You’ll also spot local faces: former WBZ anchorman Scott Wahle fleeing a building, stage actor Lewis Wheeler in a brief speaking part, and Erica McDermott —one of the sisters in “The Fighter” —here beautiful, black haired, and silent in church.

So I say see it, but know that this mythic tale has yet to be captured onscreen in all its gruesome glory, unless “The Departed” counts. That Oscar-winning 2006 film, partly inspired by Whitey and the gang, also won an Oscar for Scorsese as Best Director. “Black Mass” has a blessed long way to go.