Pretty addicting! I just wish the menu didn't close every time I leveled up. Really took me out of the flow. Or maybe having the upgrades lined along the bottom or side to click directly.
I've already fixed the menu-closing error. Now, it only opens if there's an upgrade to purchase after leveling up or when you click on the menu open button. For now, I'll leave the menu as is, and maybe in the future, I'll replace it with buttons on the sides. Thanks for your feedback!