Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
In a story so dominated by its narrator’s voice, it’s hard enough to find Poe’s tone at all, much less characterize it. But we can look for the places in the text where we are meant to know something the narrator doesn’t – this is where we see Poe crafting the story outside the realm of his fictional narrator. For example, when William reveals the telling details that hint at the special connection between him and his double – yet is unaware of this connection himself – that’s where we can see the author.
Poe might be commenting here on the nature of morality, conscience, or identity, but he does so in a manner quite the opposite of his overbearing narrator. We can’t quote this point because it’s exactly the LACK of text that condemns or condones the narrator that supports it. It is essentially left up to the reader to decide how to deal with William Wilson and his doppelganger. Doppelganger means ghostly double.