Solid gameplay and beautiful spritework !
Had some fun playing this one and there's some nice enemy variety too with the various blimps baloons and airships, and the moving clouds really add to that sense of going at high speeds in the sky, i just have one small issue with them in that they can sometimes obscure the view a bit too much, i think you should either have them with a bit less opacity or move them to a layer behind where all the gameplay happens rather than in front so you can keep the effect while not having it get in the way of the gameplay all thet much.
Other than that it's well made all around with some strong design both gameplay wise and art wise.
Good job to you guys :)