My favorite aspect of this game is the sense of mystery as you travel the caves! You could definitely make a great story out of this! I also loved the subtle puzzle solving aspect as well.
I would definitely make the pieces that you can't break a different color than the rest, so the player has a better sense of what objects can be broken or not. It seemed that almost all of the terrain in the game was breakable, which was really cool, but if you want to enhance the puzzle solving aspect, I would do so by adding unbreakable objects into the mix.
But this is still amazing nonetheless!