I would argue that the success of Iron Man (and every latch-key movie that rides on it's success, including The Avengers) hangs on two things: the accuracy in which Robert Downey Jr transformed completely into Tony Stark and the intensity of the closeup shots inside the Iron Man suit that terrifyingly humanizes a character that outwardly displays near-invincibility due to a technology advantage that outpaces his worst foe.

The marriage of this incredibly cool, technological superior suit of armor that we all not-so-secretly wish to have (of which the icing on the cake is the AI voiced by Paul Bettany) and the intensity of shots so close we can count the hairs of his beard (especially when projected on a theater screen measured in feet, not inches) is what makes Iron Man successful.

Not only is the film a bright burning star on the balance sheet of more than a few companies and individuals, but it successfully transforms a character who would otherwise be closer to unlikable and unrelatable (Stark doesn't have first world problems, he has Billionaire Problems, and not in the Weimar or Zimbabwe sense) than the empathy Tony Stark miraculously receives. The magic behind this miracle is the performance of a lifetime and the intensity of a closeup.