I like the concept and the art style. I think The enemies need some damage feedback and will be more fun if most of the enemies have only one life (in the first wave I think is a must)
The message of what upgrade the player gains is too fast. I think the upgrade system could be automatic, and give the player some choice, when the player collected a number of coins (similar to experience in Vampire Survivors), or a screen after the wave (like brotato).