The games best core strenght is that addictive gameplay. The core mechanics work great, picking the game up and playing it right away feels natural and the game creates a sense of flow immediately.
The game also does a good job with the nice pixel art look and feel.
You could have been more effective explaining the controls in the game. I just found out there is a settings menu by re-reading the page here, and X is not the most intuitive key to press to start a game anyway.
You should also focus more on giving the player a sense of progress. Passing by planets or some nice background art or giving the player constant XP for unlocking new ships might be a good addition to the game.