Clever idea, and the story seems like it could make for an interesting game. The idea of separate shadow people could make for some cool puzzles.
The control feel kinda wonky, especially since it's a bunch of 2D assets in a 3D world. I could see it working like Paper Mario does if you allow characters to move with arrow keys or AWSD but just clicking makes it hard to control depth.
The UI works pretty well, I figured out how to pick up the key and open the door fairly quickly.