I was skimming comic stuff online when I found someone complaining about the concept of female villains "needing" to be likable. Poison Ivy and Harley Quinn were used as the examples. I don't think villains in general need to be likable but they need to be interesting. I always thought part of Harleys' appeal was her not being evil like the Joker. I'm indifferent to her and don't read her books so I could be wrong. My personal taste tends to like bad guys that have depth no matter the sex.
I think Killer Croc has risen to my favorite of the Gotham rogues because of his development and more sympathetic nature. Joker is important sure, he just doesn't interest me much. Straight up evil for evils' sake is okay every once in a while although it wears thin if everyone's like that.