So I looked at the help before playing, but didn't absorb that I didn't want the zombies to collapse into particles until I finished the game. Honestly I was just marveling in the pure chaos of everything to really know what was going on, and as a comedy physics clusterbog, it works well.
However, by the second half of waves I was starting to wonder what my goal even was. Feedback on screen would definitely help. Most predominantly, showing your score on the screen instead of just at the end would really help. Also, some kind of negative feedback on killing on zombie would help you understand that you're not supposed to do that.