The narrator of Cathedral is a bitter, cynical, logical, hardened, whiney man. He views most things in life through a very non-impressed, sardonic lens. Nothing impressed him. Of his wife's ex, he writes, "Her officer—why should he have a name?" Of his wife's poems: "I didn't think much of the poem." Of the blind man's tragic loss of his wife: "Pathetic". Of his wife's attempted suicide: "But instead of dying, she got sick." Now, all of those traits don't really paint a very good picture. He is pretty narrow-minded, and not good at seeing things from someone else's perspective. Overall, he is a guy who is kind-of struggling to find happiness and meaning in life, but, also, I would say, is just pretty non-impressionable. We all know people who aren't easily touched, moved or impressed, and that seems to fit this narrator pretty well.
There are some good traits, that we see more at the end--he is kind to guests (he spends quite a bit of time with Robert), laid-back (they chill for hours), and in the end, more open-minded. He has an experience that teaches him to think outside of his own narrow-minded perspective, and it really moves him. He states in his rather straightfoward way, of his experience drawing cathedrals with his eyes closed, "It was like nothing else in my life up to now." For him, this is a huge statement, considering how stoic and hard he was before this point.
I hope that these thoughts help a bit; good luck!