I (think) I was able to figure out what to do pretty easily: dig, get gold, buy upgrades. I found the player controller a little weird to use, especially the jump being more of a float into the air. It was also a little awkward using the shop, I wasn't sure at first that I needed to press the "dig" action to use it, and at one point it did something else inconsistent. Adding some kind of friction for the player could add a lot (danger, tool degrading, inability to dig in all directions, etc)
Here's a playtest