I like how the mermaid has gills. I always wondered how they breathed underwater if they're top part was human so they had lungs. Maybe they're like some aphibians where they have both lungs and gills so they can breathe on land and underwater.
However I must mention that I was very confused when I first looked at it, it seemed to me that the gills beneath the breasts were actually the breasts themselves and therefore had a very strange shape to them. I think the breasts could be a bit more obvious because I only realised they were gills when I saw the first comment.
Love the smooth look to her tail and how it transitions seamlessly to her torso. Interesting take on her gills below her breasts! Love the armfins...would go great with webbing between her fingers, too.