In "The Fall of the House of Usher," which presentation of the narrator from the list below do you find most convincing?
1. Sane individual who finds himself in over his head as he comes to aid a friend in need.
2 Buffoon and opium user who gets absorbed into the bizarre events of the house.
3 A dreamer. The story is a retelling of a dream of the narrator.
The character of the narrator in this excellent and rather disturbing short story is definitely worthy of some serious attention, especially given Poe's propensity elsewhere in his fiction to use profoundly unreliable narrators to tell his stories. There are sections of the narrator's narrative that might suggest he is an unreliable narrator, given the way that he is subject to fancies and dreams. Consider what he sees when he looks upon the House of Usher and the tarn for the first time:
...when I again uplifted my eyes to the house itself, from its image in the pool, there grew in my mind a stange fancy--a fancy so ridiculous, indeed, that I but mention it to show the vivid force of the sensations which oppressed me. I had so worked upon my imagination as really to believe that about the whole mansion and domain there hung an atmosphere peculiar to themselves and their immediate vicinity: an atmosphere which had no affinity with the air of heaven, but which had reeked up from the decayed trees...
As he moves on, the narrator says he tries to shake off this strange feeling, which "must have been a dream." Although he does have such visions and is subject to superstition, he comes across as a rational individual trying to make sense of the scenario he has been invited to, which personally makes me feel the first out of your three options is the most likely and reasonable. Of course, it is possible to argue the other two, but for me, I feel the text suggests the narrator is a man who is desperately trying to make sense of what is going on around him, and struggling to interpret the reality of what he sees.