I really like how you combined the wooden walls that have the light peeking in with the forest-cave walls on the second floor and the blue-sky wall on the third floor! Really great!!
The light peeking through is totally something I stole :P. There's actually little bits of another kind of wallpaper in there, which cause the wooden wallpaper to make the light cracks. But since they're both dark wallpapers, it makes it looks seamless :).