Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Concerned, Loving, Lecturing, Forgiving, Teasing, Funny, Dark…
We can probably find something good to say about most of the characters we've encountered, in spite of Neil's rather judgmental point of view. (Notice that point of view looks at the narrator's perspective, while tone looks at the author's attitude toward his or her work.) Roth seems to love these characters very much even though he makes them the butts of his jokes, as well as platforms for his musings on human behavior.
Roth can be quick to give a literary spanking or two, but he's also quick to forgive in Goodbye, Columbus. We know this by the pains he takes to provide a balanced view of most characters, which is a lot more difficult to do than it might seem when you're writing in the first person.
When Roth is exploring important issues, like the discrimination the boy faces in the library, the tone seems concerned. Not to say that Roth can't get very dark—like when Neil is tormenting Brenda about the diaphragm. But, as he himself has noted, there is a deep comic intent at work. He says that while Goodbye, Columbus "has a kind of sad or melancholy edge to it, [it is] a comic book, and the situation [is] funny, very often" (source).