I don't know if you have ever read Stephen King's book On Writing, but one of the things that really stuck in my head was his description of writing as telepathy.
In essence what you are doing is very carefully crafting your own Thought and placing that down in a special format that can be interpreted by another person. All the thoughts, images and musings on themes (both conscious and unconscious), particular word choices, phrases . . . You are communicating this directly into the brain of another human being - across time and space. When you sit down to read a classic, you are opening a window into the mind of that long-dead author. Meshing your thoughts up against theirs and for a moment provoking a state within yourself that echoes that of the original creator.
Recently I have been thinking about this in terms of character. As writers we all try to craft our characters well. We want them fleshed out, with believable reactions and thoughts, consistent backstory and good dialogue. We want their purpose to be consistent with where they have come from, and their goal to echo their nature. But these characters cannot help but be an extension of what we are. The ones we like are those that have characteristics that we respect, or perhaps aspire to. Or perhaps they live the life we may dream of, strive for what we dare not. The antagonists are the opposite - encapsulating all the attributes we perceive as negative, and standing directly in the path to the hero (otherwise there would be no conflict on this level).
So these characters end up projected right into the mind of the reader. I would contend that at this point their is an immediate judgement - just as the human mind forms immediate conclusions about strangers you may be introduced to. Either you like them, or you don't. You have an immediate connection, or you are left underwhelmed. And just as the same person can either be the love of someone's life or a dull stranger (for different people), your characters can strike a chord with the book-buying public or potential editors or fail to create this response.
Now, of course there are some elements of human nature that are nearly always appealing. We love the girl who saves the kitten, or the man who cares about his friend. But when we extend to other elements of character, the reader can simply not connect with your crafted thought-projection.
In story, its the old scenario at the crit group. You circulate the story and find that two people loved the character, two hated them and four hardly care about them - and crit your word choices instead.
Have you come across situations where your characters have both connected to and underwhelmed different readers? Have you ever had one editor rave about your characters while another fails to care about them? Have you ever hunted down a book that everyone was raving about, only to find you either hated the characters or found them vacuous?
PS: I may be out of Internet range over the next day or so, will try to log in wireless, but apologies if I do not respond to posts.