Reductive design is the logical step from the old adage that less is often more. The key to this concept is that you do not put in anything that does not serve the central purpose of the character, plot, game play, etc. Just as a sentence with too many flowery adjectives become cumbersome to read, so do game design.
Having read a lot of the design thoughts and threads, I feel that some of us could use a could reminder on this concept.
i.e. in terms of plot and characterization
yes, a cliche that is poorly executed is terrible. But you know what else makes it worse? having too much stuff that distracts from the core of the character. There's a distinction here, of course, it's okay to give LAYERS. Layers of characterization means that what is on the outside still adheres to what goes on at the core. But having multiple conflicting aspects that all contradict each other, or simply adding parts that do not serve any purpose to the character? kind of distracting. i.e. if your character's whole thing is about revenge, anger, and his obsession towards it, throwing in that the guy likes pottery just seems odd. (Unless, of course, said pottery is a reflection of what he USED to be like prior to becoming obsessed with vengeance, or said hobby is somehow key to his transformation)
in terms of game play, we can see this in subsystems. While it is tempting to make a system that can accommodate over thousands of different activities and allow for exploration of the entire setting in a million different ways, there are unfortunately a finite amount of resources and time that you can put into making the game. As such, you need to be efficient in what you put in. Zero in on what is important to your design, and make those awesome. All the extra parts? either enhance them so that they can also be part of the core, or drop them entirely. A half executed idea does not work well in a finished product. (Prototyping to try out a concept, on the other hand, is okay)
I would like to propose an exercise, where we each talk about how we can use this in our current projects to better our design.