In Rebellion 2, it would be cool if the enemies got harder and harder to beat, like first you would have farmers, but you could get other foes, like Knights, Golems, Fish, and so on. You could even make a plot around it, like once the farmers are defeated, the screen would say...

With the farmers eliminated, peace has been brought back to this society, and the tech-warrior-cyber-ninjas can return to their homes. However, in the forest beyond the farmlands, something lurks in the shadows...