Since much of the poem is quoted speech, do these passages seem too unrealistic, or do they sound like what such a person might say when in a frenzy of emotion?

The poem is narrative and much of a narrative would be speech between people. However, the speech of the narrator gives us what he is thinking - he speaks to the raven hoping for some kind of response. The raven, no matter what the narrator wants to know, can only give one response: Nevermore. The narrator is frenzied, in that he wants an answer to the question of when he might next see his love. However, the raven cannot give that answer, and so the poem ends on a bitter note.