The game is excellent. Difficulty is just right. The gameplay is not mindless but you don't have to keep in mind giant logic constructions.
The only thing that could be improved is greying hints. I noticed a lot of hints which were logically "greyed", that could probably be done automatically. Manual "greying" took couple seconds to be done so that was irritating
Great storytelling concept. The soundtrack works really well, too.
Think about adding a feature of mouse-only controls. It's a preference for someone and it makes sense in this type of game.