The style of the the drawing is amazing, and the way that you drew the drawing there is alot going on in the background that it makes people look at it more and longer.The game should have these graphics in them
Try to make the characters faces have more emotion, emotion with the eyebrows and a bit with the mouth. You could also make their face tense up, which you would have to change the nose, mouth and the eyebrows.
Put some detail on the clouds and the wings on the right.
Maybe you could also make the colour a bit more solid in the necessary areas.
Take what advice you agree with and disregard what you want. This is your work and I want to keep it that way.
You are a talented artist and what ever you choose will be the essence of your vision.