Congratulations on a well made game! I was a bit confused at first when I died even though I didn't get hit. When I realised that I increment that counter in the upper right corner for every ship I kill and it decrements for every ship that I let through it quickly became a pretty frantic and fun game. One thing which I would have liked to see is some kind of powerups to my weapons. Perhaps auto-fire, or more bullets or bullets going in a diagonal direction. The music adds to the fast paced game play. Well done!

I really like this game, as it has a great pacing and increasing difficulty! It's a solid entry for a 72h game jam ;)
Here is a thing to improve in gameplay: clicking mouse button is really exhausting - it's not a tactical game, but a really fast paced shooter, and I was exhausted after clicking all the time the left mouse button, while also sometimes I used right mouse button. Usually, when you click and hold - your primary weapon is shooting all the time at "firing rate".
I like that the player's ship have visual indication of damages taken + there is health bar. In a heat of battle you must ensure player is always conscious about the ship's state, possibilities and results - I think you nailed it ;)