McMansions 101: What Makes a McMansion Bad Architecture?

Sometimes people ask, why is xyz house bad? Asking this question does not imply that the asker has bad taste or no taste whatsoever - it means that they are simply not educated in basic architectural concepts. In this post, I will introduce basic architectural concepts and explain why not all suburban/exurban/residential houses are McMansions, as well as what makes a McMansion especially hideous.
Disclaimer: These same principles do not always apply to Modernist or even canonically Postmodern architecture. These principles are for the classical or traditional architecture most residential homes are modeled after.

Design Principle #1: Masses; Voids

The mass is the largest portion of a building. Individual masses become interesting when they are combined together to form a façade. The arrangement of these shapes to create weight is called massing. As the pieces are combined, they are divided into categories: primary and secondary masses (1).
The primary mass is the largest shape in the building block. The secondary masses are the additional shapes that form the façade of a building.
Windows, doors, or other openings are called voids. Voids allow creation of negative space that allow for breaks within masses. Placing voids that allow for natural breaks in the mass create balance and rhythm across the building’s elevation.

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The secondary masses should never compete with the primary mass. 
For example: an oversized projected entry or portico (secondary mass) will overwhelm the house (primary mass) behind it.