Really love the gameplay and art! However, the connection with the theme is quite poor. The main things I think would benefit the game would be to have the enemies look more unique compared to each other. I feel like it was easy to forget which enemy was which, and not know how much health they would have. I also think having a hit animation along with invincibility frames is needed to make this a better experience.
I'm not big on the menu music, but the in game music is really awesome! The sound effects feel really good as well. The main things I would like to see would be to have some enemies drop more gold, or lowered costs of earlier upgrades, in order to have the game start off in a more enjoyable pace. Currently, the first few times you are able to upgrade, you don't have enough gold for any of the upgrades. I would also like if the mouse cursor was hidden while playing, so I only see the game cursor. Overall, this was an amazing game and I would love to see more getting added to it!