Gengar is my favorite not only due it simplicity but it design conveys plenty of emotion. You know what this Pokemon is like just by looking at it. You tell it apart from the rest. To me at least that is the appeal of Gengar. Not only that but it is a Ghost type. Ghost type are among my favorite types because they are straight forward. They aren't something you can't just figure out. They aren't something you can just define. I could go on and on but hopefully you see where I am getting at.