Your game has two main strengths, finding hidden passages and turning into a dragon!
Really liked the sense of atmosphere and lighting of the levels. I would have suggested using smoothing shading on the character + dragon, but that may be personal taste. I really liked the glowing sections on the dragon model. I had some issues with the mouse cursor not being captured (so it was possible to move it outside of the screen and I think I would definitely add a settings option to invert the y-axis on the mouse (since I'm more used to it being the other way around). Got stuck on the third level after beating all the enemies, I see there is a destructible wall but I have no idea how to make the grenade throwing enemy hit it, am I missing something? The music was not bad, but got a little bit repetitive, but I'm sure you just didn't have time to make more tracks/extend the track. Breathing fire as the dragon felt good, but the movement was a bit awkward (e.g. turning) and in my opinion he should be able to fly up/down way quicker!
As I said, I really like exploring for hidden passages and it would be cool to experience a bigger/more polished game world with this concept!