If we're going to talk about Pixar then the best film I can think of that the studio has done is Wall-E. I have not seen Up so I can't say anything about that. Wall-E however is a breakthrough and stand up achievement of Pixar's dynamism. When films were first invented they had no sound built in. Then when sound entered film many filmmakers and critics thought sound would distract image and tear the medium apart. Sound and image have not destroyed each other and have a middle ground, but Wall-E returns to this sense of little verbalism. There are mechanical sounds and environment bytes but for the first half and the bulk of the movie there is not human language dialect among the robots. In this way Wall-E is the a movie in which every person of any culture can experience the same events untouched by language barriers. It is the most mature Pixar film I've seen and touches on the current environment crisis on our planet as in the future earth of Wall-E
Pixar has come a long way not only in animation technology but story structure too. The first movies that gained them popularity was a Bug's Life and Toy Story. Although these movies had definite themes and development they only scratched the surface of deeper messages. The same with the Incredibles a lot of conformity of the 1950's and the study of uniqueness, these are big themes but the endings leave only half digested ideas for movie goers, especially the children that are the target audience.Ratatouille was the first major step to a complete theme because it was movie that taught that a man or rat can become anything he wants to be and overcome obstacles.
Pixar is company that has continually grown in ideas and concepts for animation entertainment. Studios like Dream Works reached new heights with movies like Shrek, but have not maintained a steady progression and increased sophistication within movies. In comparison Dreamworks are Cheetos against cheese on cracker with Pixar. Pixar in the forseeable future will continue to create more significant media and surprise us with better stories than before.