I tend to think that quality is something we writers judge ourselves and each other on. Quality writing, semantically, holds a different meaning for the readership as a whole. If this weren't the case all bestsellers would also win literary awards. In shaping the novel, initially, creativity reigns. Then comes revisions in which the focus is fine tuning. Making plot and characters and world all work in just the right way. Important emphasis is placed on cohesion, building (character and plot), and the sense of taking the reader for a ride. Entertainment and quality ... straying the line between the two is essential to success and yet a personal choice. This is not something with a quantity, there is no solid answer other writers can grant. Where and how to define both are up to each writer, between them and their work. Later, perhaps, editors and agents are involved in this decision, with their expertise lighting the way. But bottom line is the writer's choice in approaching their own work in a way that is at once meaningful and rewarding for him/herself. No one wants to sign their name on something their ashamed of (not to say what doesn't shame a person this year won't embarrass them in twenty years).
Just a few thoughts.