John Connolly and James ‘Whitey’ Bulger grew up together on the streets of South Boston. Decades later, in the mid 1970's, they would meet again. By then, Connolly was a major figure in the FBI's Boston office and Whitey had become godfather of the Irish Mob. What happened next – a dirty deal to bring down the Italian mob in exchange for protection for Bulger – spirals out of control, leading to murders, drug dealing, racketeering indictments and ultimately, the biggest informant scandal in the history of the FBI.

For a biopic of a real-life person, this feels like an oddly standard mob thriller. It's the true story of Boston gangster James “Whitey” Bulger, and it's told with gritty filmmaking and robust performances. – Contactmusic.com

Black Mass moves like a heavyweight, and when Cooper lands his punches they hurt. I can't imagine it's going to do much for the South Boston tourist trade, though. – The Arts Desk

Depp's performance as Bulger goes far deeper than swept-back, thinning hair and leathery, reptilian skin and delivers a soul-chilling study of sociopathic evil. – Movie Talk