I also had the mouse bug (thanks for telling me to change the sensitivity settings).
Great doom-style FPS. The in-game tutorial is perfect. The sprites are great. Shooting felt good. Movement felt good. I liked the upgrade options.
In hindsight, I wonder if we made the wrong decision switching our game to 3d models. Originally we had planned on sprite enemies as well. There's something so nice about those billboard sprites... maybe it's the nostalgia talking.
Anyways, great game.