Amazing!
I know it sounds weird but this is a GAME. Not a sample, not a demo, not a proof of concept - a game from A to Z. There are some flaws that were mentioned in other comments, but it doesn't matter. For me it was the full experience I would expect from a game.
Super story-telling. Very subtle, but with a strong and touching message at the end. One that hits you a little by surprise. Playing beautifully with the interpretation of the theme. At first I thought - "again gold, mining, etc., I know this interpretation", but the ending added great depth to it. A great example of what good design is.
Plus a list of achievements (I maxed it out), interesting mechanisms (I was swearing like hell when I saw how big the price for moves increase on the last level :D), and all in a nice UI sauce.
Chapeau bas!
If I had to add something creative, there might be more things to buy with gold in the future. E.g. bombs, as an alternative to reset in case of being stuck.
Thank you for that game!