The Unexpected Answer
The Master of "horror"? Not at all. This, very lamentably, is the label with which Poe has been imported to Europe by Baudelaire, but he was a master in whatever genre he chose to deal with: Old West adventures (e.g. The Journal of Julius Rodman), Sitchin-like science fiction (Some Words with a Mummy), Lovecraftian witchcraft (Ligeia, cf. The Thing on the Doorstep), new "Munchausen" episodes (Hans Pfaall), social satire (How to Write a Blackwood Article; Thou Art the Man!), literary criticism (The Rationale of Verse), detective stories (The Mystery of Marie Roget), psychology (The Imp of the Perverse), astrophysics (Eureka) . . . Had he lived in the Renaissance, he would now be exalted worldwide as a universal genius like Leonardo Da Vinci, rather than as a bizarre writer.
And, speaking of the Renaissance. Poe's Narrative of Arthur Gordon Pym of Nantucket, 1838, may be termed the last example of a sea "report" in the style of the 15th-16th century explorers and of Camões' long poem The Lusiads. There is a mysterious land to be discovered (the only remaining one, in this case: the South Pole), as well as commonplace "savages," earthly paradises, strange animals, surprising natural phenomena, unfair trading, etc. Of course, as a product of the 19th century, Gordon Pym reuses all such materials with a good deal of irony, though not without nostalgia for a world that was "larger" than nowadays; and as a book by Poe, it is full of horror or anyway extreme situations.
The most mysterious page in the novel is, notoriously, the last one. What's that "shrouded human figure, very far larger in its proportions than any dweller among men"? The uncanny apparition echoes the supernatural horse in Metzengerstein, written before Gordon Pym, not to speak of Red Death, after it, but there is something more to it, a cosmic awesomeness anticipating German Symbolism. Is it only by chance that Gordon Pym's voyage starts in 1827, the same year in which Arnold Böcklin was born?