I wonder what the silhouette is of?
The way everything is highlighted is odd. It all seems to have texture, but to ignore lighting. You may want to consider making your highlights all point toward your actual light source, which would be the sun, I assume, and which is even visible in the picture. It is strange indeed to be able to see the sun but to not see it light anything up (or there could be some diffuse lights just outside the picture on our side, lighting everything up! that works too....).
One last point, you may want to be carful about the transparency here. This image would look very different on a darker background, because it would change the colour of the sky. Aklso it's kind of like you haven't really followed the palette challenge, like you're using an extra colour for the sky.