Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Eeyoresque Gloom
Cheer up, Harry! The narrator of the book is pretty much always down in the dumps, going on and on about how he wants to kill himself and then giving us millions of reasons that he should be unhappy and gloomy:
He who has known the [...] angry [days] of gout attacks, or those with that wicked headache rooted behind the eyeballs that casts a spell on every nerve of eye and ear with a fiendish delight in torture, or soul-destroying, evil days of inward vacancy and despair, when, on this distracted earth, sucked dry by the vampires of finance, the world of men and so-called culture grins back at us with the lying, vulgar, brazen glamor of a Fair and dogs us with the persistence of an emetic […] (2)
Uh, yeah, it goes on. So, like we were saying, pretty uplifting, right? Er, wait…Harry is a Gloomy Gus.
Good thing the other characters have decided to give him a lesson in laughter, 'cause this guy's a downer. Hesse probably chose to use this gloomy tone because it is an extreme example of a disillusioned, middle-aged guy who just saw his nation destroyed by war. It also gives a great contrast to the tone that people in the novel like Pablo, Goethe, and Mozart take, which seems that much more playful next to Harry's doom n' gloom.