Some islands I made in Blender. 
One of my first projects. Any critiques or constructive criticism are more than welcome
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I would suggest an interesting cloud background, with some yellow, pink, or red in it. I would also suggest either adding a ground, or lowering the camera view to point more up. Some mountains in the background might also look good. As for the islands themselves, the waterfalls should be more white where they are falling. On the whole though, they look pretty good. Is it BlenderInternal, or Cycles?