Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
A really famous writer, James Joyce, once said that a novelist shouldn't make his opinions known in fiction: he should remain disinterested, as if he were standing outside his creation "paring his fingernails" (source). Reading The Metamorphosis, you get the sense that Kafka has some pretty well-manicured nails. The story itself is sensational, absurd, grotesque – but the actual tone of the story is about as dispassionate as an article in The International Journal of Electrical Engineering.