It's a bird, it's a plane, it's a … a purple and orange shape-shifting chemical compound?

Writer-director James Gunn's "Superman" was always going to be a strange chemistry of filmmaker and material. Gunn, the mind behind "Guardians of the Galaxy" and "The Suicide Squad," has reliably drifted toward a B-movie superhero realm populated (usually over-populated) with the lesser-known freaks, oddities and grotesquerie of back-issue comics.