Johnny Depp is so frustrating.

His performance in 1994’s “Ed Wood” is absolutely masterful, lending an unkillable vibrancy to Tim Burton’s black-and-white classic. He perfectly embodied the drunken antics of Jack Sparrow in the first “Pirates of the Caribbean” film.

But then came the “Pirates” sequels where Depp was merely imitating his work in the original without any of the spirit. Recent Depp vehicles such as the painful “Transcendence” and “Mortdecai” made it seem like he just doesn’t care anymore.

While it isn’t a great movie, “Black Mass” shows us that Depp still cares. With its odd narrative structure and somewhat tedious pacing, Depp’s excellent performance is its greatest accomplishment.

Depp stars as James “Whitey” Bulger, a notorious Boston crime lord who acted as an FBI informant for 20 years. “Black Mass” depicts the true story of Bulger’s rise and inglorious fall, which ended in his arrest outside a Santa Monica apartment building in 2011 at the age of 81.

Seriously, Bulger was not a nice guy. About 80 percent of the movie depicts him intimidating, beating up or straight up killing folks for any manner of perceived wrongs.

He was able to do this primarily because of FBI agent John Connolly (Joel Edgerton), a childhood acquaintance of Bulger’s. Connolly sold his superiors on the idea that turning the other cheek to Bulger’s crimes would benefit the greater good, as Bulger’s intel on other crime gangs would help the FBI gain the upper hand throughout the city.

It’s a fascinating story but one that spans a lengthy period of time without much escalation or excitement. Bulger and Connolly did a bunch of bad things for two decades before being discovered, and that’s pretty much the end of it as far as “Black Mass” is concerned.

I applaud any movie that ditches the rising action/climax/falling action formula you’ve likely seen in any literature class, but the result here is a story where the mood and stakes are mostly on a straight line throughout.

So much focus is put on Bulger’s crimes that his 16-year fugitive manhunt is almost completely ignored. That could have been an excellent second act, but instead it’s relegated to some text before the end credits.

It’s great, then, that Depp so perfectly embodies Bulger’s ghastly pallor and insidious demeanor. He humanizes Bulger enough that his hard-to-believe true crimes feel realistic.

I wouldn’t protest if he got an Oscar nomination out of this.

Unfortunately, that performance is often the only thing that carries the action. None of the individual scenes are particularly bad, but they aren’t strung together in a way that builds tension at all.

Ultimately, “Black Mass” will be lauded as brilliant by some and excruciatingly boring by others. Its dire mood and deliberate pacing make it feel like a chore at times.

But Depp is so, so good in it. For that alone, it’s worth seeing.