Whoa. This one is excellent. I do wish there were a way to get more ammo though.
That's fair. I didn't clearly communicate that losing all your ammo is the fail state. Because you have unlimited lives, you need to manage your ammo well to make it to the end.
That said, I think that I could add something like an ammo drop which would let you decide which weapon it goes to, so you can use your favorite weapon more while still being challenged.