This is a cool idea! Ammo being the health as well is good. Some variation in the speed of the enemies would be nice I think, I was able to run around until a ton were on the screen before shooting at all. Well done!
Before publishing the jam build I lowered the speed of the citizens actually with the intent to make it easier to round up many of them. But varying their speed is an excellent suggestion. I think making them a bit less predictable that way would make it more fun.
