* No clear architectural style, or a haphazard/incoherent mix of styles
* Brick or stone facades in front, and cheap siding on the (less visible) sides
* Non-structural arches and columns
* Oddly placed/sized windows
* Multiple roof lines, chimneys and dormers
To the extent that a "Recently built house in a more or less modern style" incorporates these elements, it can be considered more or less a McMansion.