When doing mysteries it's a great idea to place them on planes, trains, boats - anything that moves. Not just because these are enclosed and ensure that no new characters unexpectedly arrives or known one escapes, they also give a sense of movement. Mysteries are done best in a slow pace, however in game format that often means they come to a full stop as the player tries to figure out what to do next. The movement of the vehicle itself gives a sense of direction and progression even without demanding actual progression in the story.
Playing multiple characters is almost always fun. Playing the same timeline from different perspectives is both fun and interesting. In a regular shooter this would mean a different take on some scenes or maybe locations, but in a mystery adventure game like The Raven it means extending and developing characters. Not only do we learn more about the people we meet through dialog, but instantly pick up on differences signalling who we are in the society and who we are to the people we are talking to. It's not just about revealing a true identity, in the sense of he or she was secretly an asshole – it's more about seeing depth and idiosyncrasies of the people we meet.