The story is as engaging as it is horrifying. Poe leads the reader into the mind of a madman. Once you start to read the story you want to finish it to see what happens. The suspense is very intriguing and it has a quality that is frightening without being gory. Even though the murderer kills the old man and cuts him up hiding him under the floor, the account of events is very readable.
Its hard to tell if the narrator is just having a hallucination, as if he were in an insane asylum, or really telling the truth.
Poe, literary criticism suggests, based this story on a real murder that took place in 1830, quite creepy!
"Reaction to "The Tell-Tale Heart" upon its initial publication was mixed. The critic Horace Greeley commented in 1843 that the story was at once "strong and skillful" yet "overstrained and repulsive." Other reviewers found it "An article of thrilling interest" and "very wild and very readable."
This is a very open-ended question, but I think what you are getting at is this: what techniques does Poe use in this particular story that make him such a fixture in American literature.
First of all, in this story and in "Cask of Amontillado", Poe champions the unreliable narrator. Although using the first-person narrator was not unusual, most narrator's in the Romantic era were truthful and reliable. Poe creates the "disturbed" narrator, one that readers can both emphathize with and yet mistrust. The narrator in "Tell-Tale" is a murderer, despite all his rationalizations. We can see that in the first paragraph as he tries to convince us that he isn't insane - his nervous manner clearly indicates that he is. Then, when he is discussing the imagined sound of the heart beating between the floors, we see that his senses can't be relied upon:
And still the men chatted pleasantly, and smiled. Was it possible they heard not? Almighty God!—no, no! They heard!—they suspected!—they knew!—they were making a mockery of my horror!-
As readers, we are drawn in by the internal struggle being portrayed. The pleasantly chatting men prove to us that this sound is unheard. But we know that our murderer is losing his grip and becoming overwhelmed by it. Will he be caught? How will it happen?
The beauty of Poe is how well he crafts this crazy man. If he was not experiencing this struggle of conscience, we might not enjoy the story so much. He would simply be a villian to dismiss. But the long process of rationalization shows us that this is a man who believes he has done the world a favor. That struggle is part of why he is so capitivating a character, for all of us have been obsessed and bothered by a tiny detail at some point in our life - so there is a feeling of identification for readers, and of fear. Could we become him?
Remember, too, that Poe was one of the first authors to delve into the heart (excuse the pun!) of a criminal. Like all artists that "did it first", we remember him most. He creates the effect of suspense by keeping the length of the story short enough to enjoy in one quick sitting. He uses the internal monologue to help us identify with the narrator. He surprises us with the climatic end moment. He is a master!
Highly accomplished in fiction, poetry, and criticism, Edgar Allan Poe is one of the most distinguished American writers who has influenced other American writers for years. Turning the uses of gothic fiction to high art in such stories as "The Fall of the House of Usher" and "The Tell-Tale Heart," Poe has deservedly captured the American imagination which so loves horror and science fiction.
His artistic genius is clearly evident in "The Tell-Tale Heart" as Poe employs a technique Poe has named "arabesque." With this technique, there is a playfulness, a balance and integration, a pattern in which Poe "teases out the latent horror" of his images. In this pattern, the material images substantiate the aesthetic, and the psychological horrors parallel the physical, all of which fascinate the reader as the contemplation of the "dark side" of humanity has always done.
As an example of the arabesque pattern in which the psychological horror parallels the physical, the narrator in his bizarre reasoning contemplates the eye as a curse while the old man feels the horror that is to come:
I undid it [the lantern] just so much that a single thin ray fell upon the vulture eye. And this I did for seven long nights, every night just at midnight, but I found the eye always closed; ....I kept quite still and said nothing. For a whole hour I did not move a muscle, and in the meantime I did not hear him lie down. He was sitting up in the bed listening--just as I have done,,,,Presently I heard a slight groan, and I knew it was the groan of mortal terror....It was the low stifled sound that arises from the bottom of the soul when overcharged with awe. I knew the sound well...it has welled up from my own bosom...the terrors that distracted me.