There's been ten total Pixar movies and the last few have underwhelmed me. Cars was whatever, Ratatouille was terrible, and only half of Wall-E was amazing. But maybe that's setting the bar too high. Not everything can be a Monsters, Inc. or A Bug's Life. Having said that, Up was definitely worth watching (especially in 3D) but also nothing exceedingly memorable.
My theory is that Pixar movies with humans featured prominently ruins it. I'd prefer they humanize objects, creatures, etc. Then again, that didn't exactly work for Cars now, did it?
A nice bit about Up was that the little chubby kid was understated Asian, like he was Chinese but that was just a little side trait, which was cool. And the short in the beginning, "Partly Cloudy," was perfect and fun.
Here's an article about whether or not Kevin, the rainbow colored bird, is a nod to the LGBT movement. Also, apparently Finding Nemo had an underlying Christian message? What?!