Where do I begin. You have such a beautifully realized vision, the composition is lovely. The half-n-half helps the piece breathe, when you could have just had an AWESOME DRAGON as the only focus (not that it would be any worse for it...), and you go the extra mile with a full and *gorgeous* background. I love your choices of the pastel-like colors, too... the oranges of the dragon make him look so alive, and the purple you use to "outline" him is perfect. The soft yellows and greens really help add a feeling of distance and fantasy to the piece, and I love the bright sun making every thing bright and soft. If I could say something, I'm not sure about the harsh dark & light edges on the dragon. Don't get me wrong, it looks absolutely amazing, I just might change that next time, it feels just a tad too harsh compared to the softer edges the other structures have. But hey, I don't know, maybe it looked too fuzzy before, or it's the style your looking for, let me know!
But there's the aspect beyond the technicalities, the story, choices, and the history in this. I love the city in the back, it looks ancient and mystical. Very Greek inspired, the towers look almost carved-no... formed from the floating rocks through magic, or some very dedicated workers. I even like the floating rocks, you do a good job giving them enough shading and texture but not going overboard. If you twisted my arm, I'd say maybe a few more slight details on the city? Nothing much, maybe an extra few small windows, nothing to call too much attention to.
The dragon though... wow. He (or She?) is just so GRAND, I love it! The sweeping curves of the horns, wings, the protrusions on it's arms, it's wonderful! The claws just coming out of the I like the shaping and feel of the head, the broad chin gives it a stern and proud expression that add so much to the character. The horns and frill being one long plate around the skull is something I also like, it being one long unending line is so creative and striking! I also adore the large oval scales, continuing the shapes on his wings. Speaking of wings, the floating sections of his wings add so much presence and mystique to the creature. Coupled with his similar colors to the rocks and the floating wing sections, the dragon looks like some mighty elemental guardian made from the very rocks surrounding the keep, molded and formed into a mighty creature by the inhabitants to only allow the worthy to pass. That's just me, though.
All of your work I've seen is insane, and very inspiring for a young artist like myself. It's brilliantly done fantasy work, and this piece is no exception. I'd love to make work like this, and the few minor critiques I have in no way diminish the quality of this epic piece, here's to many more!