I love the brush work on the body (mostly the tail and fins) It adds a nice lively texture. The colours are good, the yellow on the torso is quite nice and helps to create some volume and focus point. (although I think you can push it even more)The details on her hair (and the design!) are well done! The contrast between the sharply painted hair and the soft shading in the rest of the figure seems a little to abrubt tho. Your values could use a little work but overall but it is definitely in the right direction. If you want, I can do a paitover for you to point out some mistakes. (Let me knowThe main thing that I think would improve the image, is indeed the background. You don't need a super detailed background at all, but a small changes like: making the background darker towards the bottom, maybe adding some floating specs or some vague shapes in the background will make a huge difference.One last thing, If you add her other arm into the painting behind her, but colour it lighter (more blueish as the color of the water), you can add a lot of extra depth to the image without much effortI hope this is of use to you. Goodluck with the awesome painting and let me know if I can help you out with a paintover!