When my wife recently read a passage of my latest novel, Path of Darkness, and visibly recoiled and grimaced I got excited. When she told me that the creature in question was gross and disturbing, I was elated. Mission accomplished.
I have always enjoyed great bad guys in fantasy and sci-fi; Darth Vader, Sauron, and the demons, Reaper, and Jakara in the Shannara series. The juxtaposition between the good of the main characters and the evil and threat of the enemy serves up the most exciting and sometimes poignant moments in stories.
We all want a clear bad guy. I think it gets down to this; if we have a clear enemy, a clear antithesis to all we understand as good and moral, the easier it is to decide on your path in life. Not only that, but there is the feeling of success when there is even the smallest of victories. As simple as speaking a kind word and giving someone your time when the enemy inside wishes nothing but me, me, me.
Fantasy allows me personally to live out and visualize my desire in life. Live morally and fight against the evil in the world. The bad guys in the best of this genre celebrate the hard, drawn-out struggle of good vs evil. The best is never easy, never pretty, armor is torn and wounds inflicted. Without the pain and hardship, the sweetness of success when it finally comes would be lost.
I love a good bad guy when those that struggle against it/them never give up though grief and loss gathers close around them and threatens to pull them down. The art of writing a bad guy that can and should destroy the hero is allowed to show its power before coming to its end by the combined desperation of good.
Without desperate struggle against evil this life and these novels would be extremely dull.