To me the best part of writing is creating the characters. As the story unfolds, I get to know them better and often they surprise me, taking the story in a different direction than I'd originally planned. Once I set up a scene where one character tries to talk the hero out of running off to rescue the innocents. The story line had the hero ignoring the advise and leaving anyway. However, once I wrote the dialog, I realized only a stupid man would leave at that time. Since the character I created was not only brave, but highly intelligent, I had no choice but to rewrite the story line.
For me to continue to read a book, I have to like the main characters. They don't have to be perfect, just have redeeming qualities. I don't enjoy books written from villain's point of view. I don't want to see into the mind of a serial killer or rapist. I'll tolerate a few chapters, but not the whole book. Even on TV or in the movies I can't stand a whiny, stupidly indecisive, or just plain annoying heroine. Horror movies where the girl does nothing but scream and weep drive me insane. Usually it doesn't take long before I'm rooting for the villain to just kill her and put us all out of our misery.