Both are written from the first person limited point of view. However, the narrator in "The Fall of th House of Usher" has contact with other characters whereas the one in "The Pit and the Pendulum" does not. Therefore, the character who is an invited guest in a friend's home is able to glean more information about his surroundings and circumstances than the prisoner in held in isolation.
Both stories, however, have brusque surprise endings, easily accomodated for by the limited point of view of the narrator. In this way the surprise of the narrator is also that of the reader, who "lives" his experiences (in a chronological way) along with him.