Poe is generally known for his melodramatic prose. But “William Wilson” is one of the few Poe stories that is surprisingly cheese-free. This might be because the story is about issues of conscience and morality, rather than blood and gore. In this way, the style sort of fits the story. You’ll notice that, for the most part, these sentences are calmly composed and even prosaic at times. Prosaic means having the style of prose. Of course, there are a few passages of exclamations and ornate, horror-stricken prose (see the first paragraph, or the last paragraph, or that paragraph in the middle where Wilson leans over the sleeping face of his double). It just wouldn’t be Poe without it.