A good pitchdeck condenses a complicated subject to its essence, just enough text to convince and short enough to avoid wasting time. It informs rather than overwhelms, and stays clear of hyperbole. It's the equivalent of a telegram, it conveys information, and every word has a cost.

A bad pitchdeck is one that focuses on form over function, wastes the readers time with unnecessary detail and extrapolates into an unknowable future with too much conviction that things will really play out that way (they won't).