Simple and fun! Really, really good.
Not letting up/down shoot really enhanced the gameplay, the weapon evolution, it's a good touch, the monster are great too!
If you want give it a try to my game: https://kailcor.itch.io/donutchaox
Fixed version: https://kailcor.itch.io/donutchaox-fixedversion (the commited one do not start for unity compression.... XD, big fail).