Lenses are an idea I first saw put into practice in the Amber Diceless RPG, which presents several versions of each of the major canon NPCs. This allows the GM to choose which lens to view Corwin through (just how much of a bastard is he?), for example — and just like taking off or putting on a pair of glasses changes what you see, which Corwin the GM uses makes a big difference in the game.
This same idea is used throughout GURPS Illuminati, which offers up different big picture explanations for every major conspiracy. Is the Priory protecting the bloodline of Christ, or aliens who are secretly living among us? It depends on which lens the GM chooses, which is awesome for keeping your players on their toes.
More games should use lenses. In fact, I’d argue that every RPG that features a central storyline of any sort should offer a variety of ways to approach the major elements of that story.
But is this concept useful in home games, too? Twisting it around a bit, I can see presenting multiple views about a major NPC (through in-game events and other NPCs) and letting the PCs decide how to approach them — but that’s not precisely the same thing. What do you think?