Very cool game! The way you've utilized the models and shading to create a dark atmospheric game was excellent. Here are some things I think you can improve upon.
- Consider adding a short story at the beginning of the game to explain to improve immersion. Why is the player collecting ghosts? What are the differences between all the colors?
- Ghosts are a bit hard to find. Consider adding slight hints to make them easier to find.
- Camera sensitivity can be an issue for players with high DPI. Adding clamping can be a quick and straightforward way to provide a consistent experience. Not an issue for the game dev as the player can also be at fault for using a high DPI, but something to consider in your games.