Finally! I've been waiting for this essay since the "In Defense of..." idea was announced. Good show, GT.
It is this feeling of the action scenes carrying the family dilemmas with them as the story goes on that makes it more than just an entertaining action film. One can identify enough with the characters to invest in them emotionally.
You're right, there is an incredible sense of the characters in this movie. And it's not like it goes to great lengths to explicitly "develop character," it uses the subtle moments, the quiet moments, and the voices of the actors to really flesh them out and then holds that tension through the action scenes. For a
medium, such as animation, that is quick to use stereotypes and flat characters as a kind of storytelling shorthand, here is an animated film that isn't afraid to spend time with the characters and really delve into their world on a level that is more than superficial animation. Pixar has always been detailed in their approach to animation, but in this film they have come to the point where the details are not just in the lighting of a cityscape or on the scuffs of a doorframe, but in the strengths, weaknesses, insecurities and dilemmas of their characters and how they deal with them.
I would probably put this one at the top of my list, as well. Of all the films I've seen from 2004 (so far), this is the one that seems to hold up best and still be just as enjoyable as the first viewing. This really is a great film. Nice job.* Edited to correct the incorrect usage of a word.