This is the first Poe story that resembles the notion of the "prose poem," which has no Aristotelian complication as such, and exists only to paint an unusual mood.
The basic scenario looks forward to "The Masque of the Red Death." It's narrated by an individual who styles himself "the Greek Oinos," and when the story opens, Oinos and six unnamed men are seen sitting in a room getting drunk, while Zoilus, a man of their former acquaintance, lies dead of plague. A strange shadow enters the room, and speaks to them:
And the shadow answered, "I am SHADOW, and my dwelling is near to the Catacombs of Ptolemais, and hard by those dim plains of Helusion which border upon the foul Charonian canal." And then did we, the seven, start from our seats in horror, and stand trembling, and shuddering, and aghast, for the tones in the voice of the shadow were not the tones of any one being, but of a multitude of beings, and, varying in their cadences from syllable to syllable fell duskly upon our ears in the well-remembered and familiar accents of many thousand departed friends.
This sort of mood-piece, with its emphasis on a "vague and formless" shape, possibly influenced H.P. Lovecraft's conception of his formless terrors, though HPL's terrors weren't usually direct representations of Death.