I noticed that you included Harley Quinn in the poll, even though she primarily isn't a videogame villain. In that case...I would probably write a love letter to Haman Karn.
I don't know why, but there is something in her bubblegum hair and "queen ***** of the universe" (I know Kerrigan came up with that one, but I think it fits Karn as well) attitude that I find extremely loveable. It helps that she is one of the few people to completely unnerve Char.
But you know, one suprising thing I realised is that there aren't that many really likeable female villains (for me, anyway). Most of the time, when I try to think of female characters that I like, they are either among the heroes or at least neutral. Bizzare, really...