This is a really nice atmosphere you've captured. I'd to see more art in this vein.

I love the atmosphere, there is something both strange and poetic in it. The way you placed the planets in the background doesn't work though. The big one on the right is almost cut in half by the wall, the small yellowish one and the star both make a tangent with the wall, all that contribute to the disturbing sensation these elements are laying on the wall and not behind as they should be. 

That said I would totally play a game with such a mood :)

i really like what i did with the planet and i wanted to show it off, but i ruined it with the big text over it :P

I agree with hzoltan :) ; nice atmosphere in your piece by the way

I like this mockup, but the preview picture tells nothing. If it wasn't intentional, maybe you could change it to the astronaut, it's well drawn to be on the focus. But this is just one oppinion :)