Taste and temperament are the obvious answers, but that is not the good that I refer to. What elements move fantasy from mere delusion to something uplifting?
What makes a fantastic story inspirational instead of a siren call?
I look around and see so many men buried alive in paper and have to wonder if the lore they consumed was deadly to them.
Is this the work of the zeitgeist, the method of delivery, or is there poison in the myths they read?
Perhaps the true heroic narrative is unknown to them.
Perhaps the combination of extreme discipline and wild fortunes that makes heroes in reality is rare in the stories they choose.
If we take the hyper abstraction of reality that most fantasy is and boil it down to its more grounded elements, perhaps we would find that the good narratives have ingredients that lay out a path to greatness rather than day dreaming about it.
Does this speak to the character of the author?
It certainly displays their presuppositions.