Really nice game.
It was quite difficult and I didn't realize I could unlock more ships after completing all the levels. Replaying some levels after unlocking new ships made the game easier. Maybe you can add a "New Ship Unlocked" message in level end screen.
Also, sometimes I got a little confused on pressing left or right, especially when the ship was on top. It would've been easier if the ship stayed at one location and the level rotated.
Overall, great job! Good Luck! :)