Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
On the one hand, Bigger is a thoroughly unlikeable character. Even though we recognize that it is not his fault that he’s poor, and we recognize that circumstances have created his tendency towards crime, he’s a manipulative bully. He’s mean to his little sister, mean to his friends, and mean to his girlfriend.
Ultimately, however, though we don’t like Bigger, the tone of the novel is sympathetic to the position he’s in. This is achieved in large part by a narrator who explains how shame and fear dominate Bigger’s life, causing him to act the way he does:
"Mr. Max, a guy gets tired of being told what he can do and can’t do. You get a little job here and a little job there. You shine shoes, sweep streets; anything... You don’t make enough to live on. You don’t know when you going to get fired. Pretty soon you get so you can’t hope for nothing [...] You know, Mr. Max, I always think of white folks [...] Well, they own everything. They choke you off the face of the earth. They like God. . . ." he swallowed, closed his eyes and sighed. "They don’t even let you feel what you want to feel. They after you so hot and hard you can only feel what they doing to you. They kill you before you die." (3.1084-1087)
No matter how horribly Bigger acts (and he does act horribly), moments like these allow the reader to understand—and sympathize with—the vice-like mental strain that would cause someone to panic and lose hope.