Mystery games. For a very brief time in the 90's, I remember when there was a small surge in interactive storytelling involving murder mysteries or large crimes. You'd start to play, and the game would randomly assign who the perpetrator was to a character, and reorganize the clues and dialogue accordingly. You'd have to investigate, but since most games trying this were on CDs and cheap attempts at video capture were all the rage, you wound up with games like Ripper where you had Christopher Walken screaming at you and Karen Allen acting nowhere near as awesome as she does in Indiana Jones movies.
Plus, once you pick up on what changed in the story, it's usually pretty easy to figure out who the bad guy is.
More modern games have tried to do larger stories with a mystery reaching through, but once you play those games once, there's little replay value in doing it all over again. Examples of this are Heavy Rain and L.A. Noire.
So when I found a Nintendo DS game called Nine Persons, Nine Hours, Nine Doors (or 999 for short), I was intrigued. A mystery with multiple endings based off the choices you make, and while I was hesitant about the game just randomly changing who the bad guy was based off of stuff I picked (looking at you, Ripper), I figured that it was an obscure Japanese game, there must be some hook to it.
Twenty minutes in, I was hooked.
