Although simple game, I liked it. Great idea, maybe would work better on touch, so would recommend putting this on like a mobile phone and you could have a popular small game in your hands! Audio worked well on top of the game play as well!
One thing I would change or think about is the rocks that blow up into smaller rocks, that maybe they would always explode in a way that the smaller parts would go towards the middle. Also that maybe they only take like a second of your clock, or something like that, because they would do less "damage" in a sense.