The desert terrain looks nothing like a desert. It's lumpy, muddy looking piles are completely uncharacteristic of a desert. They don't pass for rock outcroppings or mountains either, so I'd say you need more of a windswept sand dune approach. The photoshop stuff is alright... mostly cliché. Keep trying though.
E: as for your text on the back cover, you need to avoid the unfortunate tangents, such as how "...a new" intersects with Sonic's eye and covers his whole arm, and how "begins" completely covers his lower jaw.
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