I'm not sure why, but on the first launch the game crashed, on the second launch it worked, though.
Fun game and nice concept, the only suggestion that comes to mind is that I wasn't too sure if i was hitting enemies properly, or if they needed multiple hits. Some kind of player feedback like an HP bar overhead of enemies, and for the death maybe a sound effect or spawning a animation when they die, which could be a particle, a image, or just a sound effect. I've noticed when replaying it that there is in fact a hitmark, the red sphere, but i feel like the typical X that pops on hit (as a reference in call of duty games) would make it more subtle.
Great job! I hope this helps, cheers :D