Things I particularly like, in the order I noticed them:- 1) Somehow it captures being underwater better than average. I think it's partly the light, partly the way the model's hair appears to be floating rather than hanging (and for once there's a reason for it to float). 2) The subtle scale effects on her skin, most noticeably on her left arm and the left side of her neck and face. 3) The single best painting of a jellyfish in water that I have ever seen. (which isn't to say someone hasn't done better; anyone who reads this and thinks they know of one should answer with a link)
Thank you so much for your observation. I took my time to go through photographs of women underwater to understand the way hair move in water. The jellyfish is a brush, I painted over it a bit to make it look more magical and glowy.