Designing around a core mechanic

The author presents a "Core Diagram" for game design, placing the core mechanic, the most frequently used purposeful interaction, at the center with secondary mechanics, progression systems and narrative forming outward layers. The article says the best games have a strong core mechanic that is easy to grasp, with each layer gating the one outside it and giving context to the layers inside. It applies the model to Super Mario Bros., Portal, Flower and fantasy RPGs, and argues that Angry Birds has awkward, arbitrary links between its layers while CityVille's inner layers are tightly woven but its narrative is weak.