This is a really fun little game! I like the way the gameplay mechanics force you to prioritize the red-core enemies over the blue ones. The music also fit perfectly with the visuals.
If you wanted to improve, I suggest adding shadows to show where the red-code guys are going to land, I got crushed and he just kind of bounced off my head. Make an enemy landing on you an instant kill and that would make it super intense. I also suggest adding a way to shoot upwards, a number of times the blue core ones would be to high for me to hit. Lastly, when the ship is loosing altitude or gaining it, you should have the clouds in the background move up and down to reflect that change.
Overall great game, with a few small changes, I think this could be amazing!
Check out my game if you get a chance!