What makes a McMansion bad architecture?

From the Worst of McMansions Tumblr:

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.

Note that McMansion refers to a large modern house that is considered ostentatious and lacking in architectural integrity, not McDonalds restaurants architecture, which is fairly interesting in its own right. The concepts outlined in the post are useful ways to look at all building types.