i played on the casual level. good hint system. it is about an enemy that collects humans in order to live. he gives them a choice of becoming one of his soldiers and accept his dark pact and become a puppet for him or die. he took your sister and you are trying to find her.
i played on the custom level. good hint system. it had a shape shifter enemy. it was capturing people's essences to live forever and increase it's power.