Genghis Khan: ruthless killer or great military leader?

Genghis khan was a ruthless killer, despite his few examples of mercy. He built an empire based on violence, and the principle was surrender or die. He never made any attempt to negotiate for lands, he simply took what he wanted. Genghis committed his first murder at age 10, showing that from an early age concern for other human life was not one of his. While in command he would often order the barbaric taking of ears or other parts off of the conquered corpses. Although I respect him for creating the largest land empire ever created, I still consider him a barbarian because of the way he acquired these lands. If a ruler today were to conquer large amounts of land through military power we would call them a ruthless tyrant, so why should Genghis khan be treated differently?