Our impression of the narrator is largely a matter of opinion, but it is informed and guided by the author's choices in depicting him throughout the poem. It would be a much easier argument to state that the author seems melancholy, morose or depressed, than to say that he seems cheerful and optimistic.
On the surface, the poem is about a man grieving over a dead woman, Lenore, and a seemingly supernatural raven's appearance. It seems unclear whether the raven is actually speaking to the narrator, and choosing to say "nevermore", or if this is simply a sound that the raven makes, with no intended meaning. There is a key distinction that takes place in the poem depending upon our interpretation.
The narrator poses emotional questions to the raven; will he be reunited with Lenore after death? Will the raven stop tormenting him? If the raven is a supernatural creature that chooses to say "no", then the raven seems to represent death, fate, and powers that are beyond man's control; the narrator becomes a meek and powerless castaway in the ocean of destiny. If, however, the raven is just a bird, and the narrator knows this, and expects the bird to say "nevermore" regardless of the questions that he poses to it, then the narrator becomes something of a masochist; he asks questions that he knows will emotionally hurt him if the answer is "no". This is a completely normal part of the grieving process, but it may cause us to interpret the narrator as someone who is actively seeking to be hurt.
Personally, my impression of the narrator is that he is simply a normal person going through the grieving process, and he sees the appearance of the raven as a mysterious and unknowable reflection of himself, and the powers of life and death; things that he cannot control. This is a cathartic experience for him, to receive answers to questions that no human can answer; will he be reunited with Lenore after death? No. Now that he has that answer, perhaps he can "move on", so to speak.