Two stars, Rated R. 129 minutes. The last time I interviewed Ben Affleck, about his smart, spirited CIA thriller “Argo,” he shared the outcome he dreads most when making a movie: “Everybody walks bovine-like through the turnstile going, ‘Yeah, it was OK. Yeah, it was OK.’ And you stamp a ‘B’ Cinemascore on their head and that’s the goal.” Those words — so admirable and on-point in this age of regularized mediocrity — take on particularly haunting resonance when considering “Live by Night,” Affleck’s fourth directorial foray that, despite a promising pedigree, lush Prohibition-era atmospherics and Affleck’s stellar track record behind the camera, can best be described as OK. This isn’t to damn Affleck’s intentions: He clearly hasn’t set out to make the kind of banal, impersonal multiplex fodder he decried.