Woah!
Oh mah gawd, this is awesome! I'm really glad you decided to turn that sketch into a finished piece! It seriously looks really great! I think it's so good that I'm forced to nitpick a bit to try and offer any kind of useful critique on this one.
I dunno how well this would work, but maybe you can try making the dragons farther in the distance a little paler next time, to try to add a bit to the sense of depth. It might give it a little bit of atmosphere too, with a slight sense of haze in the air.