I've always liked morally grey areas in stories, I think it's good being able to debate characters/ factions actions to a certain extent. I've never liked bastions of good and kindness or people who are evil for the sake of being evil.
I wrote a story about a man who gave the order to commit a war crime and being in his mind is interesting I think, because of his guilt I think it makes him kind of redeemable. I don't know really, I love seeing how characters react to certain events.
!PIZZA
Yes, agree. The strange phenomenon that the characters suddenly react in their own ways is one of the most rewarding parts of storytelling.