Beautiful game! I do have two big thinks, if you're interested.
Other people have commented on this, but the controls are not very intuitive. Why click to shoot if you can only aim by moving left and right? Why 1 and 2 instead of Tab, i.e. why use three buttons when one will do?
Second, consider what message you're sending to the player with how you present different elements. Why do destructible walls look like indestructible walls look like retractable walls? Why does the goalpost at the end of the level look like an obstacle?
Otherwise, great work! It was fun and I was a little sad when I ran out of levels to play.