Owen Gleiberman Chief Film Critic There’s a standard road map for an actor like Sylvester Stallone — at 76, still looking good, but no longer with a body made of rock(y) — to enter the comic-book movie zone, and that’s for him to play a figure like the righteous Ravager Stakar Ogord in “Guardians of the Galaxy Vol. 2,” or to voice King Shark in “The Suicide Squad.” That’s all likable nostalgic novelty casting. But what if Stallone, who in his way has played invincible superheroes for decades (think “Rambo” and its sequels or “The Expendables” and its sequels), wants to go full avenger and portray a total comic-book demigod? He’ll star in a chintzy slice of hellfire like “Samaritan,” based on the Mythos Comics graphic novel that was published in 2014. It’s set in Granite City, an everyday dystopia where Stallone lugs his body around with a reluctant roughneck shamble. He plays an aging crime-fighter-in-hiding in a movie that as written by Bragi F. Schut (who also wrote the comic) and directed by Julius Avery offers a conventional but downbeat, minimally plotted but maximally incendiary variation on bare-bones superhero action.