I actually was lucky enough to get to see this at the Pixar location about a week before general release as I have a buddy who works there.
I liked it, but thought it seemed a little boring in the beginning/middle of it. I was pretty tired, so I am sure that doesn't help
btw, it is amazing how much goes into these movies. Pixar was full of all the concept art/scupltures/progressions of characters/storyboards/etc. Very impressive.
Overall, I enjoyed it, despite it seemingly slow for a while.