Apparently, John Singleton’s “Four Brothers” is meant to be a righteous throwback to the blaxploitation genre. Which is a mistake. The big secret about early blaxploitation movies like “Super Fly,” “Shaft,” and “Black Caesar” is that they’re not very good. In fact, before the genre wigged out around 1974 and started making truly freaky films like “Three the Hard Way” and “Dolemite,” most blaxploitation movies were downright boring.

Mr. Singleton is faithful to his source material in one respect, at least: “Four Brothers” is a slog.

The first person we’re introduced to in “Four Brothers” is the sainted mother of the titular brothers, Evelyn Mercer (Fionnula Flanagan). She’s a salty old dame whose tough love is tempered by a mischievous gleam in her eye. I found her insufferable. When, five minutes into the movie, two thugs gunned her down in a corner store, I instinctively leapt to my feet and offered to hold the door so they could make a quicker getaway.

Unfortunately for fans of good movies, Ms. Mercer’s death brings her four foster children back to town: Mark Wahlberg; the singer Tyrese Gibson; “Troy” boytoy Garrett Hedlund; and OutKast’s Andre 3000, billed here as Andre Benjamin. The boys are bad to the bone, and they’re back to find out who splattered mom across the linoleum. Their investigative technique: Publicly attack random strangers who give clues that lead to the next bad guy; repeat until end of movie is reached.

Slowly (oh so slowly) it emerges that not only did Ms. Mercer’s death have something to do with Mr. 3000’s dream of building “luxurious offices,” but also that she will be making ghostly appearances throughout the film, dispensing wisdom and twinkling her eyes like some kind of demented leprechaun. Eventually we’re introduced to the villain of the piece, Victor Sweet (Chiwe tel Ejiofor), who owns a laughably fake restaurant with a red-on-red color scheme right out of “Black Caesar.”

In the final 20 minutes, the scenes pile up and zip by, transforming the film from a boring bad movie to a watchable bad movie. Besides Mr. 3000, who is terrific at reading cue cards, and Tyrese, whose bulky presence grows on you, the cast is blandly capable. Mr. Wahlberg’s performance comes across as a tutorial on all the different ways you can strut onscreen.

Of moderate interest is the fact that the movie’s token good cop is played by Terrence Howard, the lead pimp in the Mr. Singleton-produced “Hustle and Flow.” Also, Mr. Hedlund, who first appeared playing Achilles’ gay lover, Patroclus, in “Troy,” is relentlessly gaybaited in “Four Brothers.” I don’t think this is a clever meta-commentary on the film, however. It is simply idiotic.

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“If German Cinema is to conquer the world it must boast actors who can become household names. I’m not going to relax until we’ve made real progress in this area.” This snappy line comes straight from the mouth of Dr. Joseph Goebbels, Hitler’s minister of propaganda and the subject of the German documentary “The Goebbels Experiment.”

The film is illustrated with amazing archival footage, but every word of its narration is taken from Goebbels’s diaries. The result is a Goebbels-eye-view of the Third Reich, from the early rise of the National Socialist Party to the final desperate days in the Berlin bunker, with a voiceover by Kenneth Branagh.

Mr. Branagh follows Goebbels’s diaries as he swings from elation to blackest despair, sometimes in the space of a single sentence. Magda, his wife, is “my goddess,” and suddenly she is “so hard on me and cruel.” “There’s no one to help me,” he moans during a dark few days. “I don’t want any help anyways.” German documentarian Leni Riefenstahl is a “lunatic,” and Winston Churchill is a “disgusting fat beast.” Later, though, Dr. Goebbels decides he “isn’t quite as stupid as Chamberlain.”

But the movie’s “star,” Mr. Branagh, is also its biggest problem. He reads the diary through clenched teeth, with barely controlled mania, transforming even the most banal comments about the weather into the rantings of a lunatic. This seems to go against the filmmakers’ stated intention to present Goebbels without any editorial comment. Their documentary is fascinating, but it’s nothing you couldn’t see on the History Channel.