I personally believe it involves a perfect combination of three things: Great story, a lot of "wow" moments. and yes, good viewing. This is part of the reason I think a lot of people actually prefer DHS's Fantasmic, because it blends these 3 things rather well. And even though as a pure show Disneyland's is clearly better, the stadium seating at DHS makes it almost as popular.
So what do you think? What are the ingredients to a perfect Nighttime show? What is your favorite nighttime spectacular, and what makes it your favorite?