Overall, very impressive! Did you draw teh ground scene too? If so, was that a photoshop rendering or did you scan previous artwork in? It's very beautiful .
Critique: Maybe my perspective is off, but the glow of sunlight in the background arcs... is that supposed to be the world's atmospheric crest? The arc seems very tight for a world horizon. If it's not, ignore. Like I said, I may be missing the perspective .