I agree, the trailers and promotional material for UP had me worried - but what a lovely and dare I say it UPLIFTING film! And for my money, the pure visual storytelling in the first act put Wall-E to shame for sheer emotional impact. (and that is saying something!)
So, I will venture to offer one observation that could be construed as negative - but only just. I was amazed at how well the movie introduced its fantastical elements gradually, thus achieving an amazing level of willing suspension of disbelief. There was only a single element that ran up against my UN-willingness.
Everything else, I was delighted to buy into - and I still give this the highest honors. Time will tell where I stack it, but it's clearly going into the top tier of Pixar achievements.