I'm indifferent to Y'shtola, personally. I'm inclined to think she's popular for the same reasons as Jaina and Sylvanas are popular in WoW - and much like those two characters, I feel she's long since overstayed her welcome even as characters with greater depth and potential have been put on the chopping block.

She mostly gets points from me for looking like an adult and behaving like one - which is probably a low bar, but it makes her stand out from the likes of the twins and G'raha.