Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Dark, Melancholy, Confused
You don't need to read beyond the first chapter of Big Sur to determine that this is a dark novel. The first half of the first sentence sets the tone:
The church is blowing a sad windblown 'Kathleen' on the bells in the skid row slums as I wake up all woebegone and goopy, groaning from another drinking bout and groaning most of all because I'd ruined my 'secret return' to San Francisco by getting silly drunk while hiding in the alleys with bums." (1.1)
For a novel that deals with delirium tremens, mental and spiritual breakdowns, and severe alcoholism, this beginning is to be expected. As far as our label of "confused" goes, remember that Jack may be writing in reflection, but that doesn't mean that he fully understands what happened. In fact, he makes a point of telling his readers, explicitly, several times, that he still doesn't get what went on in Big Sur (more on that in "Narrator Point of View"). This confusion is reflected in the novel's tone. Jack isn't some enlightened guy looking back on the foolish days of his youth; he writes with an immediacy that keeps the waters – and the tone – just a bit murky.