I love this concept and think it's very fun as it is already. Two suggestions that would take it to another level: 1) I saw this in the comments below, but grid-based movement would make this much tighter and snappier. 2) I would have liked some better feedback on whether or not I hit the "enemies" correctly, with like a little "tick" if I shot it with the wrong shape, and better positive feedback when I hit it successfully. There were a couple of close calls when I couldn't tell if I hit them or I took damage. A health bar could help this as well.
Great job. I had a really good time.