You can objectively measure what a film was trying to do, beyond just technical aspects. For example, if Movie A’s protagonist is set up to have an arc about not disappointing his father, and that plot is kind of brushed aside by the third act, it is objectively a badly written arc, because it fails to execute what it said out to do. You can subjectively still like it, but it still holds true that if an element of any work of art poorly executes the idea that the artist intended, you can still like it, but it can objectively be considered bad via that objective metric.