Reus is about shaping nature and about the greed of mankind. You control mythical giants, through which you control every aspect of nature. You can perform feats like terrascaping, creating life and genetic manipulation. However at one point humanity enters the stage and they escape from the control of your giants. You can still change their environment or create oceans underneath their cities, but you can't change their will. The challenge is to let mankind and nature live in harmony, while you encounter the many vices humanity has to offer. This means that as a player some of your tasks are solving human wars, countering deforestation and even surviving attacks againts the giants themselves.