Throughout the setup, John is forced to interact with characters who could not be more different from John in some way or another. And just as the color white looks brightest when put next to black, just as noise seems the loudest when it follows silence, the contrast of these traits makes John's personality stand out far more than it would on its own.
We don't get to see Holly Gennaro's face for almost her entire opening scene. Instead, we get the back of her head. But we can tell a lot about what kind of woman she is by what she is doing- she is bustling through the corridors of Nakatomi Corp, keeping a laser focus on her work in the middle of the office Christmas party. Before we see her face we know that she is driven, tough, and may put way more focus on her work than her relationships.
I find John McClane's opening shot to be the most interesting because rather than communicating what John is, it tells us what he is NOT. When an audience comes to the theater to see an action film, they come with certain predisposed ideas about the protagonist. They expect the stereotypical hard-as-nails badass, a man without fear, always willing to shoot first and ask questions later. But our first shot of John McClane is of his hand gripping the armrest of his airplane seat in FEAR. Although John may act tough and stoic when he relates to people, we know from this opening action that John does not have nerves of steel. He is capable of fear, anxiety, indecision. This one shot helps establish the type of person John is at the start of his character arc compared to what the events of the story turn him into in the end. (Remember that John remains reluctant to take on traditional action hero behavior until halfway through the movie. Until then, he tries to hide from the terrorists, arrest the terrorists, and avoid shooting the terrorists.)
(sorry about the crappy formatting. I can't figure out how to get it right on blogger)
INT. LIMO – DAY