It's impressive how you made a solid shop system and a tutorial in a week! The game in this state can get repetitive and a little boring after you finish the 1st few levels but it has a lot of potential. I think one of the best features of top down shooters which make it so fun is the game juice/feel. Huge particle effects, camera shake, loud crunchy sfx, enemy death sequences- I feel like the game would feel so much more fun with these. Basically, go all in and experiment with player feedback. A way to keep track of enemies' hp(like an hp bar) would also be good since I can't really tell if I'm getting close to killing one and an aim line thing(not sure what it's called) to help the player know where they are shooting would be great. Maybe a way for the followers to respawn after they die would also be good since it feels like the game is pushing me to fail when most of my followers die even tho I still wanna win. The formations would also be a lot more useful with more followers in the area.
Sorry if this comes off too pressuring or harsh, but I just see a lot of potential with the followers + shooter mechanic. The game was still quite addictive and fun to play and I really did enjoy it!