I absolutely love this game. I have been thinking about making something similar for quite some time, and this is much better than what I am currently able to do.
I like the wind sound and the adaptive sound track. The music is great, I found myself walking around for while even though it was slower and less interesting just so I could hear the music. One thing I could suggest is that often I would go back and forth between walking and flying, and the transition between the two themes felt almost like an interruption or like the music lost its place. I think it was because the musical theme often did not get to resolve before it switched. I think that if the instrumental balance changed when you switched between flying and walking, but it didn't change musical themes until whatever section was playing finished, it would make the transitions sound smoother. I also think it would be cool if there were distinct night and day themes, it would go well with the difference in lighting to enhance the atmosphere.
The dragon's animation is so fluid and dynamic, it really adds to the immersion and makes the dragon feel alive. The wingtip trails were a little distracting, but the trails in the air were more subtle and helped give a sense of the speed. The coin particle effects in the dragon's lair and the sound for breathing fire were very satisfying. Overall, this is an excellent prototype that well deserves further development.
This game has earned a follow from me, and I hope you keep working on it and add more content in the future.