If Johnny Depp’s mesmerizing performance — a bracing return to form for the star after a series of critical and commercial misfires — is the chief selling point of Black Mass, there is much else to recommend this sober, sprawling, deeply engrossing evocation of Bulger’s South Boston fiefdom and his complex relationship with the FBI agent John Connolly, played with equally impressive skill by Joel Edgerton.

This is Depp’s show all the way, featuring his best dramatic performance since another organized-crime movie, 1997’s “Donnie Brasco.”

Scott Cooper’s Black Mass is a big, brash, horribly watchable gangster picture taken from an extraordinary true story and conceived on familiar generic lines.

Johnny Depp’s broodingly psychotic turn as convicted Boston crime lord James ‘Whitey’ Bulger is not the only tasty thing about Scott Cooper’s tale of the unholy alliance between a South Boston Irish mobster and the FBI.

Depp's instinct for observing, underlaying and keeping things in, then letting it all out when required, pays big dividends here in a performance far more convincing than his previous big gangster role, John Dillinger in Michael Mann's Public Enemies; it's unexpected, very welcome at this point in his career, and one of his best.