Loved this game, the one I had the most fun with so far!
I think something could be improved here and there. For example, I would like more clarity about stats, for example how much damage I do and how much damage an upgrade grant. Also legendary upgrade are just too strong, nullify the challenge after you buy one or two.
In my opinion the graphics are not bad, but some elements should stand out more. For example enemy and projectile are almost the same, the player character has almost the same color as the background...
Also you could add an explanation about how interest work, I figured out it's like how some auto-chess game works (cool idea btw, it works very well!) but it's not clear at first.
Overall it's a very nice game, good job!