I love character development. I almost can always figure out the way a story goes from start to finish not even halfway through. Despite that, I love going through a story and seeing the characters be fleshed out, pulled through the wringer, challenged, cared for, grown, and changed through a story. It could be any character, the old guy across the street or the friend of the protagonist or even the antagonist for all I care. I like the way the worlds are grey and people screw up and I like the way a plot develops the character. Whenever you succeed in that, hooray for you.
I also kind of like a fic that can express friendship and romance at the same time (my god impossible I know) but I can dream.