I second the motion to tone down the colours, they are, at this moment, far too saturated. Even opening GIMP/Photoshop and adjusting the saturation slider could really improve this, though you might end up needing to up the contrast too, sometimes weird stuff happens. Manual swapping is, of course, preferred. I also suggest transition tiles between the land and ocean, this will add alot to the piece without even being that much work. As with any piece, the potential is there, you just have to work at it. I also have to ask - why does the top 'Treeling' have single pixel eyes when the rest have mario mushroom-esque eyes?