This is a great idea! I love the combo of tetris and digging. This has a lot of potential, but (as I'm sure you're aware) It needs a lot more polish.
Things to add:
-Menus
-Better digging controls. I think just clicking the block you want to dig would be easier (This might just be me cause I'm new to mouse and keyboard)
-Music and SFX. Preferably Chip tune and electronic sounds to match the art
- A clearer goal. This one might not be so obvious but for someone just picking up the game its hard to tell what exactly your trying to achieve until you find the first skeleton. You did a good job showing to me through the animation and its dissapearance that the bones are what I was trying to get but until then I was left wondering what to do.
- A story. This one isn't as neccesary. It could be as simple as you're an archeologist searching for bones but I would like to see how you could explain the rocks falling from the sky through a story.
After all that plus maybe an unlock system or some other form of progression you've got a fun little game you can release. I hope you continue with this idea in the future. I'd like to see where it goes!