I love the concept. I felt especially clever when I could shoot the bullet for one kill, cross the screen barrier to the other side and pull my bullet back to me for a second kill. You could really expand on this. Maybe slow down the pacing at first to allow new players to get the hang of it.

Fun submission. I think it could benefit from some more complex theming (maybe you're throwing a boomerang rather than recovering a bullet) and sprites, but it's still fun how it is. It's rather hard and some level geometry might have helped the strategy aspect as well. Good job!