I looked at it for a while and finally decided what it was that had been bothering me about it, though; like some of the other comments,it's the craters. The amount and crispness of crater overlap looks really strange to me.
Amazing work! The earth and the moon look great. If I were to make a criticism I would say that the moon has a few too many craters on it and it seems that some of them overlap each other. But regardless a great piece of work!