Cool! I like that the water rises on the island when it recedes from the beach! And I like the colours you've used. I think you could improve the palms by making it clear that the light is coming from directly above (hence the shadows directly below) and probably getting rid of / reducing the dithering. The combination of stripes and dithering is not ideal here, in my opinion. Hope that helps. 
Thank you CELS. It certainly helps to be told this :) I am a slow learner because I learn by doing things wrong for far too long and than suddenly waking up and improving haha ^^
I try to work with your feedback and I would on a logic point of view totally agree with you. No discussion at all. For me it is just weird like this. Somehow I have to feel instead of thinking to make the "final" step of learning :)
So I apologize if I will do things wrong still. It does not mean I did not get your feedback. I thank you very much for commenting and presenting it. Let's hope improvement comes sooner than later.