Thank you so much for the feedback! The reason for the ammo pickup system is to force the player to move by not just killing the enemy but thinking about when they should kill the enemies. However, I should make the ammo pickups more common and easier to pick up, what do you think about that?
Also, your idea about adding enemies dropping ammo is quite interesting. I could make their spawn rate dependent on how many missiles the player has (fewer missile = more "blue enemies") to make the game more engaging for players who have difficulty picking up ammo, definitely something I need to think more about.
Once again, thanks for the feedback!