First off, let me mention the first thing that came to mind when I watched this film: It's extremely rare to see not only a movie, but an adventure movie, and an animated one at that, which has an elderly man as the main character! For that alone, Up
breaks new ground.
The story itself is very original. In an attempt to live out the adventure he's always wanted, Carl decides to tie a zillion helium balloons to his house and fly off into the sky. But since we need that character dynamic that a lot of movies thrive on, a little kid accidentally gets added to the mix. Russell is overweight, and he too breaks new ground: an overweight adventure protagonist who's portrayed positively.
Both characters are played for humor at times, with Carl's crotchety "old man who doesn't like people" nature as well as his old age, and Russell's lack of athleticism (to a degree) played for laughs and even some cartoon slapstick, but both characters also get their chance to shine later on through some nice Character Development
Like other Pixar films, Up
touches on some rather heady themes. For one thing, it's strongly implied that earlier in life, Carl's wife Ellie had a miscarriage. It's not stated, but you know what happened. And Carl - and the audience - gets another shock: his childhood idol, the man who inspired him to go on an adventure in the first place and started his love for adventure, is in fact evil and has been killing everyone he met who happened to land in his place!
Above all, though, this is a movie about adventure, with a great deal of clever humor. The way Carl and Russell attach Carl's floating house to their bodies as they explore the land so the house doesn't fly off is one heck of a surreal sight. And many of the characters are just great. The pack of dogs who can talk via translator collars are a lot of fun and a great source of humor. They act very human-like, but their dog natures overpower them, and it's funny hearing their speech go from "I got you now!" to "Squirrel! Squirrel!" And there's still Disney-style cartoon slapstick, particularly involving the exotic bird the two find on their journeys.
is what a lot of movies can be at their best: multiple moods that form a cohesive whole. It's funny. It's tearjerking at times. It's adventurous and exciting. And it's refreshingly original.