What makes The Incredibles stand out from Pixar's other computer animated features is that it's the first to be written and directed by an "outsider". Brad Bird, who also made the fine 1999 animated film The Iron Giant and was one of the core team of The Simpsons, has an approach that, while hewing to Pixar's taut, twisty story aesthetics (no surprise, since, like the rest of the main Pixar guys, Bird went to CalArts), has more of a sense of individual vision. (You will note that he is the sole credited writer for the film; in the past, each Pixar releases was credited to a team of writers.) Another difference is that this film, while family-friendly, is geared more towards adults (its PG rating is due to much comic book-style violence), and the mere fact that Pixar finally made a film about human beings instead of toys or fish is an undisputed milestone as well.
The Incredibles is about a husband-and-wife pair of retired superheroes who, along with their similarly gifted children, are called back into action to defeat an insane supervillain. Pixar's structural evolution is evident in the film: You're dealing with a dysfunctional family. The story is far less gag-related than other Pixar movies. There are no Randy Newman songs (or songs of any kind). And it doesn't try to be cute. On top of that, The Incredibles has even less to do with the maudlin superhero movies of late and feels more like a James Bond film, with its gadgets, secret lairs, sexy femme fatale, and derring-do. There are also obvious influences from both Raiders of the Lost Ark and the early Star Wars films (especially the sound effects, and a high-speed chase through a forest that's almost a shot-for-shot ripoff of the scene in Return of the Jedi).
One thing that has stayed consistent with Pixar's previous output is that these guys are smart enough to know that audiences don't need a big Hollywood star to provide a voice. So whereas other studios bend over backwards trying to get you excited about Will Smith or Ben Stiller lending their vocal talents, Pixar knows you'll see their movies simply because they make good movies: The Incredibles' big names, Craig T. Nelson and Holly Hunter, are hardly box office draws. I'd like to see more of that, please, where a voice actor is cast only if they're right for the part.
All that said, The Incredibles may not make my top ten list this year, since more interesting, oddball films have been released in 2004, and there are a few flaws in the human animation that are a little distracting (chief among them the characters' lipless mouths not fully suiting the dialogue), but so what? It looks fantastic and it's fun to watch. What more do you need?