The features that might make one mystery more fascinating that another are: Predictability; Resolution; Clues available; Surprise; Novelty and Details.
Explanation:
What makes a mystery fascinating is the inability to explain some facts and events in rational way or how they challenge the explanations we have of how the world works with a scientific explanation or logic reasoning.
But the features that makes one mystery more fascinating then another includes how predictable is the story; if there was a resolution; which clues and details were known about the mystery; the level of surprise and novelty in the case. With all this features one mystery still might be very difficult for human understanding making it really fascinating.
