I suck at games like this and only passed a few levels. I'll give this another go, but here are some early impressions.
I like the music and the way mood changes completely once you enter from menu to the game. Gameplay itself is fluid and works nicely. Ship movement and overall tempo of the battle are good, but levels could be shorter.
Constant enemy fire encourages you to stay on left and play passive. At least I was mostly focused on dodging projectiles, so hitting enemies was just a matter of luck. Some short-term goals such as collectible power-ups might motivate the player to wander more. They would also add variance to gameplay.