I don't know what it is but I'm right there with ya.
Part of it, I think, is that Zee's C-lister status has allowed writers to give her an actual personality while characters like Diana must be all things to all people. At the same time, her association with both Bats and Constantine keeps her in the limelight much more than other C-listers so we get to see that characterization more than most.
I also like that her design tends to emphasize her legs and hips more than the typical comic obsession with balloon tits. Hey, I love tits too but it gets old when every character has the same dimensions. And some artists draw Zee as very busty as well, but most seem to get that she is more about the overall form, that she could be modestly endowed and emphasizing the ladies with her clothing instead of being G cups.
In my mind, Zee is Dita von Teese. She isn't an especially handsome woman, her facial features are a little plain, but she cleans up very well and she knows how to *behave* womanly. Zee is a stage performer similar to Dita and would know how to sell the performance, she would exude sexuality when needed.