Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Compassionate, Intimate
There are lots of different ways an author can use tone with a third-person omniscient narrator. Jonathan Swift, for example, decided to be mean and sarcastic. But Toni Morrison chooses to be understanding and compassionate. She gets us close to people—not in order to make them saints of villains—but to show them as real, flawed human beings.
In fact, just the sensation of closeness makes us feel more warmly towards these characters than we otherwise would have. We can get a sense of this intimacy in passages like this one, where Morrison talks about the people sleeping in Valerian's vacation house: "Down below, where the moon couldn't get to, in the servants' quarters, Sydney and Ondine made alternate trips to the bathroom and went quickly back to sleep" (2.29). Nothing more intimate than a midnight restroom break, right?
The superhuman ability to be awake while every character in the book is asleep helps establish power we readers have compared to the characters. But with great control comes great responsibility, and Morrison isn't going to make it easy for us to judge her characters as either good or bad. Characters are complicated and contradictory, and Morrison always uses a compassionate, intimate tone to convey this without becoming overly critical.