Don't get me wrong, Pixar's characters are still drawn for us with care, just not great care. Only old Carl is given a full background, while his young traveling partner, Russel, was only given some brief lines of dialogue regarding his deadbeat Dad. Even the villain is merely given a brief newsreel before he shows up a full blown madman later on in the film.
Other than these small details, much of the film felt unbelievable. It may sound ludicrous to talk this way about an animated film in general, but pretty much all of Pixars other films gave us a feeling that we were part of a sort of alternate reality. Either a fantasy world unknown to the real world via Toy Story, and to an extent, The Incredibles, or completely fictional universes like Monsters Inc., Cars etc. This film felt grounded in the real world that Carl faced from the start, and then just out of the blue decided that real world rules don't apply anymore (flying balloon house, crazy undiscovered world in South America, giant undiscovered bird species, talking dog collars and much more) All of this was fun, but felt slightly misplaced against the film's initial backdrop.
Overall, however, this is still a strong entry into the Pixar catalog and only a minimal slip in their otherwise stellar output.