Well, it's kind of hard to show a deep story in a two minute long trailer.
Not really, they just have to add things that keep you guessing. Just a two- second clip of something that makes the story seem more than what it is.
This is how the age of "casual" gaming came to be. Pleasing everyone in video games has always ended catastrophically.
That depends on what you're adding in. Like I said, just the right elements are needed.