I really love the background, I think it's perfect. Maybe you could do something with the tree in the foreground, so it would match better? At the moment it sticks out a little, like it was from another picture.
Whatever you do, I'm sure it will be really cool!
While I thought all the comments and suggestions were nice, I really like the sort of otherworldly feeling the piece has, partly because there's no evidence of life. It seems like a really quiet, peaceful place.
Just my opinion!