I like how those sharp piles draw the viewer into the picture. So perspective has succeeded well!
I personally would've done something to the foreground too (some grasses or rocks etc.) but since this is a warmup piece it's fine as it is now.
Shading and atmosphere work here very well! :)

Love your art, especially the colours and arrangement of the objects.
Did you ever think about drawing some Dune related stuff?
Huge desert sandworms and such.
I think it would be epic.