The sprites are pretty good, if you could add some death animations and a transition when the game restarts it would feel way more polished. I almost missed the sounds and music until I saw the other comments, because it is very quiet. The gameplay was ok, but I had some problem with the controls.
There is a limit on (most?) keyboards to how many and which keys you can press at the same time. In mine, for example, I cannot press right+x+c at the same time, so I could not shoot in that direction while standing in place. Adding WASD as a second option for movement (and maybe F+G for shooting and standing) would have helped.
It also says that it can be beat without hurting anyone, but I tried and the ending was the same. At least a little message or icon in the same ending screen when no one was killed would have made it different and worth the effort.