Well done, I really liked the graphics and sound! I suggest you change the controls to make the ship rotation faster. Also, adding some different weapons, other types of enemies would be nice as adding a goal to a game (not just infinite defence). You can expand the area - allow the player to move far from the planet, add some random loot in space and the player will choose between leaving a planet for a long time for a nice bounty. All in all, nice work with a space for further development!:)