Well, what do you expect? Left 4 Dead 3? This is just a 2d platformer game with a shooting mechanic. But we will be very glad if you would like to try it.
You need to survive the wave which will be increasingly difficult. And get the highest Score. The Enemies which fall out of the view will spawn at the top again. But you as a heroic guy, will die with honor for falling off from platform. That's all i guess.