The Borders for the Screenshot are really Choppy, and the back doesn't look that interesting, Why don't you try using an outer glow or something ? The Front looks fine though , And Good Luck in the Competition !
Ok, the others pointed it out: The borders are choppy and the ingame screens get rather small, don't they? Other than that I'd say you should change the fonts on the back. The one on the top is... okaaayyh, but I the one beside the sonic heads is really overused and dull.
The front is really great though, I love these retro-boxes! Keep up the good work!