Loved this one!
Everything is great. Only missing music, but the game loop is very fun and addictive so it's not a big deal.
My suggestions:
- A little more feedback when digging. Maybe something like minecraft "breaking" animation. Specially when you have no upgrades.
- Since the digging is all made in a grid, the character movement would feel better if it was locked on the grid too.
- Just add a "Game Over" message when the player reaches the bottom
Overall, very good job, I've enjoyed this game a lot!