See. This is good criticism.I don't think the "ruthless" or " gory" aspects of a ninja movie is an issue here. Sadistic and gory fight scenes are a common theme in ninja stories( Think Ninja assassin or the phenomenon video game Ninja gaiden). The main issue is the story. You should try to put all these ideas that you've mentioned into a coherent screenplay. I know it may seem unnecessary to you right now, but trust me, when you try to actually WRITE the stuff on a piece of paper, everything changes. You'll realize you need to do so much more than what you initially thought. A small example : you know the general premise but do you know what your actors will specifically say in each scene? Going forward just with the flow of each scene usually doesn't result in a good story.