I think the figure/ground relationship might need a bit of help here. In my opinion, the ground below is a bit too crisp and focused. I would Gausssian blur that to get rid of the detail and blur it forcing a more narrow feild of focus onto the floating island.

I would also suggest changing the icon color instead of the tower color. That would tie the seprate structures together a bit more and have them mirrored nicely in the central tower area as well.

Great stuff so far