The story follows reluctant protagonist Carl Fredrickson, a 78-year old balloon salesman, who along with his now-departed wife, always dreamt of flying to adventure in Paradise Falls, South America. During a moving, poignant montage of his life, it becomes clear that the opportunity for adventure is passing the couple by. So when the widower Carl is sued and his home threatened, he takes the opportunity to take off, the house held afloat by thousands upon thousands of colorful balloons for the adventure he never had. All goes according to plan until he discovers Russell, an overeager "wilderness explorer," has stowed away beneath his porch.
The second act is the film's weakest, and the adventure advertised boils down to a few paltry miles. After a brief storm sequence, the unlikely pair find themselves on the other side of the canyon, but nevertheless "three days" from Paradise Falls. With the floating home strapped to their backs, Carl and Russell begin their trek, only to be sidetracked by the obligatory supporting characters, amusing though they may be: "Kevin" a fictional female dodo-like bird with hilarious favoritism, and "Doug" a golden retriever with a dog-to-English translation collar.
Where the film finds itself in trouble is in keeping the established themes at the forefront of the story when the arbitrary sequence of events in the second act unfold. The villain, Carl's childhood idol (which makes this guy how old?), a disgraced adventurer by the name of Charles Muntz, is the perfect match as a man who's been corrupted by his dreams, but he's never developed to a satisfying level and receives relatively little screen time.
Muntz's minions are a wellspring of only occasionally successful gags, an armada of translation-collared dogs tasked with hunting down Carl, Russell, and most importantly, Kevin. Their presence in the film feels somewhat random, and not quite funny enough to justify. It's becoming an ironically dirty word in reference to Pixar's work, but it all feels a little too cartoony.
The visuals are as strong as the best Pixar has offered, though shot composition gives everything a sort of flat feel to it (a problem perhaps 3-D was meant to rectify), with characters seldom moving on more than one plane, leaving the environments feeling oddly like stage backdrops.
"Up" is sadly Pixar's last original film until 2013, but with its glaring screenplay problems, it may be for the best that the studio recharge its creative cannons. After ten feature films, nine completely original, it's hard to leverage complaints against "Up" greater than that it simply isn't their best work. It may not be the revelation that "Ratatouille" or "Wall-E" were, but middle of the road Pixar is still worth the price of admission.