The audio in this game is awesome. From subtle music to crispy sounds of gems - awesome!
Visuals are also very pleasing.
For the gameplay - I like the addictivenes of these mine-and-upgrade games. It is nothing original, but it works. I was almost missing some end goal, but then I found it.
What I was missing was the theme implementation. I kind of liked the idea of upgrading light source, but it just doesn't make any sense to me that you build a lighthouse in the underground caves.
I definitely had fun playing this game. Good job!