Well, first off let me tell you that the idea for this is truly incredible.
Put more effort into the planet.
The walls and oher painted stuff looks like a good basis for TONS of detail that you could add.
Add tiny little details in that part under the arch. That could be a city far away...
Stars? Add them up top. ^.^
I really think this piece has so much potential it is incredible, just never stop adding detail to it, it could become something of pure wonder.
looks nice to me i love the dark figure contrasting with the BG. love the colors and composition. but i think you could have put some more detail into the clouds and the rock(?) walls, they look flat when i compare them with the planet in the BG.
but if you gave the planet that "painty" texture you gave to the rest, that'd be nice too.
More details as :tigaer: said and maybe change the moon's colour to something whiter to make it more realistic. Also - unless you intended to make the figure look like a midget - the proportion could be improved. Finally put more textures on the tree. Contraty to what I said, this is a beautiful compostion.
Overall I like this image very much, and the "Star Wars" feel is pretty cool. The moon and the dusty clouds are perfect, but the rock structures need some work. Compared to the other sections, the rocks look a bit slapdash and unfinished, and I know that's not your style. Unfortunately, I don't know very much about how to paint in photoshop either, so I'm afraid I can't give you technical advice on how to improve. All I can say is to keep experimenting, and hopefully someone else will come along who can help you better.