What I liked: I found a surprising amount of risk/reward and quick thinking in this game. Often I would rapid fire shots going for a quick kill but I sacrificed accuracy and risked missing all of my shots. A nicely lined up head shot can take forever to connect but is almost an instant kill. I loved the challenge of balancing exactly how long I should keep control of the bullet.
What I would suggest: I think making it viable to shoot enemy bullets out of the air would add some much needed defensive options. The current system of giving health per kill makes the game drag on and can give you so much health you will never die.