Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Invested; Skeptical, Scrutinizing
Let's be honest. Utopia is not filled with dramatic emotion, but that doesn't mean our faithful narrator Thomas More doesn't care deeply about what he's hearing, or for that matter, that Hythloday doesn't care about what he's describing: they do! Doesn't this sound like someone who's invested in what he's hearing?: "'Then let me implore you, my dear Raphael,' said I, 'describe that island [Utopia] to us!'" (1.41). See?
At the same time, that is about as emotional as anyone gets in this book. The main characters are all invested in coming to a philosophical and ethical conclusion about the state of government and social well-fare, so they need to remain both skeptical and scrutinizing so that they can think clearly about what's at stake. If they freak out about something emotional, it's going to be hard for them to construct effective arguments.
Even though More enthusiastically urges Hythloday to describe Utopia, More ends the dialogue still weighing what he heard and not letting himself be swept away: "When Raphael had finished his story, I was left thinking that quite a few of the laws and customs he had described as existing among the Utopians were really absurd." (2.110). While it might not be the dramatic conclusion we've been craving, it leaves the reader in the same thoughtful frame of mind as the narrator. We should be left thinking over Hythloday's story, too. And boy, are we.