Some figures of speech include:
Allegories- The moss growing outside of a decaying estate which was formerly grandiose and sumptuous; the dead sister; the inevitability of Usher's appareance, and the fall from glory of the House of Usher are all allegories to fate and its control over our lives: How the influences that we cannot control at times end up taking up our inner self, and then spits us out.
Anaphora- The repetition of words or phrases within one same paragraph in order to balance out the narration and enhance the storytelling process:
I looked upon the scene before me–upon the mere house, and the simple landscape features of the domain–upon the bleak walls–upon the vacant eye-like windows–upon a few rank sedges–and upon a few white trunks of decayed trees
Many minutes, many hours, many days, have I heard it
Alliteration: Poe describes many things using the same first letter such as the words:
feeble and futile
icing, a sinkin, a sickening of the heart
Rythm: As with everything Poe writes, he always wants to give balance through rhyme:
Oppresicely, melancholy, destructively, agonizingly, etc.