These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Mary Sue: A very interesting case. Can Mary Sue, perhaps, be done well? Istra (Psyche) is undoubtedly perfect in beauty, temperament, goodness and love; yet because this is one of the story's initial givens rather than its point, because she is not the main character, and because the main character both loves and hates her for it, this fact adds dimensions to the story rather than flattening it.
An additional complication is added by the fact that for much of the story the main character believes - very reasonably believes, as she points out in her denunciation of the gods - that Psyche is delusional.