I like it.
The concept of a city on a floating rock in the sky is an interesting one.
The background and the rock have been given a lot of attention and depth but the city could do with a bit more to make it stand out more ( despite the fact that it's already the center of attention). Also the shading is great and gives the scene a sort of ominous feel.
Nicely constructed; cool concept. 75/100 B+