Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Shaw gives all of his characters a fair shake. In his preface he declares that, "There are no villains in the piece." All of the people at Joan's trial end up convicting her for understandable reasons (at least from their point of view). Her former friends who abandon her to death don't lie about it or anything. They tell her straight up that they won't help her if she tries to free Paris on her own. She knows what she's getting into. Then there's Joan, herself. Rather than making her the perfect one dimensional heroine, Shaw draws a rich and complex character. She's brave, proud, funny, sentimental, and faithful. Shaw's refusal to reduce his characters to melodramatic stereotypes elevates the play to the level of high tragedy.