It gets them thinking, and has them trying to solve a problem. Mystery movies are good because they are suspenseful. People feel like they are put into a real live situation where they are the detective, and they have to figure out the problem. They like to finish the puzzle themselves. I also think that people like to be freaked out and baffled by the mystery.
Mystery stories are so much different than love stories and adventure stories.
What makes mystery stories so different from other genres, is the way that the problem is solved. In adventure stories and love stories you pretty much know what is going to happen in the end. Like who is going to end up with who, and what is going to happen to who. In a mystery story you think you know what is going to happen, but you don t really know the truth. Sometimes it ends up totally different than what you thought it would be, and that is what keeps you on the edge of your seat.