The United States Conference of Catholic Bishops publishes movie reviews, rating films on this scale:

• A-I — general patronage;
• A-II — adults and adolescents;
• A-III — adults;
• L — limited adult audience, films whose problematic content many adults would find troubling. L replaces the previous classification, A-IV.
• A-IV — adults, with reservations (an A-IV classification designates problematic films that, while not morally offensive in themselves, require caution and some analysis and explanation as a safeguard against wrong interpretations and false conclusions);
• O — morally offensive.

I am interested by the notion of films requiring analysis and explanation as a safeguard against wrong interpretations and false conclusions.
They gave Serenity an A-III.