Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Sober
The narrator in this book doesn't tend to get very bent out of shape about anything that's going on. You're not going to see many exclamation points. Instead, you're more likely to get a plain tone no matter how intense the action is. In the last line of the book, for example, the narrator tells us that Madame de Rênal, a main character, "did not try in any way to shorten her life, but three days after Julien, she died while hugging her children" (2.45.51).
Wait, what? That's how it ends? No explanation at all? Yup, that's just the kind of tone Stendhal gives us. Stuff happens. Deal with it.