I love the art and it's a great start to a game!
I see it going a couple of ways. A whack'a'mole type scenario where have 3 horizontal slots for windows or other things to appear. You can slide horizontally to hit the 3 different slots. Then windows appear and you have to smash them before they disappear, otherwise you lose a life. Also sometimes things that aren't a window appear, such as a puppy, and if you smash them then you also lose a life.
OR going down a rhythm based approach as I found it fun to smash in time with the music. Windows come down from the top and you move horizontally to smash them as they come down, smashing them in time with the music.
Nice job!