Awesome!! Sure ^>^ here is some feedback on ways to improve :)

I would make a size difference between the melee and the ranged enemies in this case, because it's very hard to tell them apart. Making the ranged enemies a bit smaller would help. When hovering the mouse over the buttons, having a tooltip appear with some information would also improve things a lot! I currently have no idea how much exactly the upgrades are affecting the stats of the monsters Another subtle but big improvement would be adding a range indicator on the monsters you control, so we know exactly how much range the ranged monsters have as well as the melee ones.

Those are my main suggestions on how to improve this game! Other suggestions moreso involve ideas for expanding the game itself (level completion, level select, a skill tree to make future runs more dynamic and stuff etc), but for the scope of the current game itself, these were the main ideas I felt are worth sharing! :) Ah- and lastly, some sort of timer that shows when the waves start, or a button to control starting the next wave / starting early

I hope this helps!