Really cool game, It's got an awesome aesthetic!
Probably the most important thing that the game needs is some good juice and feedback for when you attack the enemies, because for a while I wasn't even sure if my attacks were doing anything. A good sound effect, maybe make the enemies flash white for a fraction of a second, and maybe a special animation would greatly help to improve this.
Also, some additional variation would be nice, such as new enemy types or pickups or upgrades, because right now each wave is pretty much the same.
Overall, I had a lot of fun playing, and it's actually very immersive and has a lot of charm. Good job!