I like the tombstone-mechanic, adds an extra layer to it. And the lighting is nice. Good job :)

I got 124! I think it would be more fun if the spawn rate increased dramatically as the game progresses, because the only added difficulty is the persisting tombstones.

But it is well made and efficient! Well done.

I really like how you added an additional layer of interest by making the tombstones left by the enemies solid instead of allowing the player to pass through them. It meant I had to be a little more strategic about where I was drawing the enemies, lest I catch myself in a killbox made of the bodies of my enemies! Another nice detail is the lighting effects produced when the player fires shots.

Excellent job!