I like it! Despite the simplicity of the mechanics, the game is incredibly addictive. I think this would make a fantastic time-killer if you expanded it a bit. For example, it feels like it’s crying out for a movement speed upgrade, because by the end of a level you spend more time just moving around than actually digging. Then you could add different block types, transitions between levels, and so on.
The only thing I didn’t like was the sprite for the danger entity that chases the player. It looks so crude that it’s not even clear what it’s supposed to be. It might as well just be a white rectangle with “!!DANGER!!” written on it.