Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Humorous, Reverent, Intimate
Since most of the chapters that comprise this novel were originally published as separate stories, the tone shifts as much as the genre—at times humorous or mocking, at other times serious, even reverent.
The humor's most evident in "Was," where Faulkner describes a raucous failure of a chase and uses caricature to mock the bachelor uncles and the woman who pursues them. In fact, everyone is being chased in this story—slaves, bachelors, and foxes.
Since much of the book gets inside the heads of the characters, the tone is also very intimate. Look at this:
"[...] he opened his eyes and lay peaceful and quiet as a child, looking up at the motionless belly of rain-murmured canvas upon which the glow of the heater was dying slowly away..." (6.63).
Or this:
[Edmonds] stood beside the car and watched Lucas cross the Square, toward the stores, erect beneath the old, fine, well-cared-for hat, walking with that unswerving and dignified deliberation which every now and then, and with something sharp at the heart, Edmonds recognized as having come from his own ancestry too as the hat had come. He was not gone long. He returned, unhurried, and got into the car. He was carrying a small sack--obviously candy, a nickel's worth. He put it into Molly's hand. 'Here,' he said. 'You aint got no teeth left but you can still gum it'" (2.3.2.70-71).
Instead of judging his characters coldly from a distance, Faulkner presents their conflicts and their good and bad moments from within an intimate space. Again, this doesn't mean that he's making the bad guys look good, or undercutting our judgment of them. On the contrary, the intimate tone opens up the possibility for understanding different shades of this otherwise "black and white" subject.
There's also an overriding tone of reverence throughout the stories, particularly when Isaac is pondering the mysteries of the universe and the oneness of man and nature. But Faulkner manages to convey his wonder about people in general, with all their foolishness and awesomeness. The long, rambling sentences that travel from the past to the future, the sweeping descriptions of history and culture—all these seem to say, "Can you believe how amazing this all is?"