Hm, I would elevate the horizon line just a tad. Seems a bit lopsided at the moment. Good work on the reflection on the water though. The purple rocks are a bit too saturated (the next color, which looks like a skin/peach, is too saturated as well, more so than the purple). I would actually recommend losing the dithering on the rocks -- but ... this kinda depends. In the context of the piece I would say it doesn't work and you should go with smoother shading. Hm, maybe change the perspective of the beach so that it curves to the end of the picture (like a quarter circle kind of line).