What is the style of "The Tell-Tale Heart"?

Poe wants us to get inside the tortured mind of a murderer, the better to understand him. The style in which he writes "The Tell-Tale Heart" constantly pushes us to an emotional response in the hope that we will feel greater empathy. This illustrates how Poe tries to make us complicit in the foul deed that has been committed.
The style of "The Tell-Tale Heart" accurately matches up with the protagonist's character. The protagonist is not simply the story's narrator; he is an unreliable narrator. Further, he is an emotionally unstable narrator. The use of this literary device heightens tension and makes us more engaged with the story as we try to get the bottom of what's really going on. As the narrator is chronically unreliable, we have no alternative but to keep our wits about us as we attempt to get at the truth.
Although the narrator constantly tries to assure us that he is perfectly sane, Poe's stylistic approach to the story suggests otherwise. The narrator often speaks in short, sharp sentences. We, as readers, are frustrated. Such sentences tell us nothing about the narrator except perhaps that he is far from being the paragon of sanity which he'd have us believe he is. But the failure to reveal much in the way of information also encourages us to read on, as we are anxious to find out just what the narrator is hiding.
The narrator, in his increasingly fevered state, also addresses us directly. Again, it is as if Poe is somehow implicating us in the murderous actions of the killer/narrator. We've been chosen to be privy to the innermost secrets of his tell-tale heart and in the process opened up our own hearts to a dark, disturbing drive buried deep within the human psyche.
The use of syntax and punctuation is very important in this regard. Poe uses exclamation marks, dashes, repetition, and countless protestations of sanity as part of an attempt to make us see what the narrator sees and hear what he hears. As the contents of the narrator's tell-tale heart are revealed, so are those of our own, and at long last truth through empathy can finally emerge.