The graphics are homogenous which is my favorite part about your game! Otherwise, I think that you could have implement multiple columns for different level difficulties (I stopped at level 4 so tell me if I'm wrong). The idea is not so bad with more variety probably fat people who need 2 burgers etc. There is a bug in which if two clients are too close from each other, one burger will deactivate both and they will only take one burger even if you shoot back at them. I don't know if it suffices them to eat one burger, that is not my point: it is not clear who needs burger and who doesn't. Otherwise, the game idea is great, but its implementation is too simple.