"WALL-E" was a technically brilliant movie. Take a featureless, ovoid shape and give it a strong character using only audio, 2 changing shapes (eyes), and two sticks/weapons (arms) (I would mention the hands, but they were not integral to shaping the character). Very well done. Then the sheer amount of assets for the movie was incredible.
I have to say though, I think "UP" had more for the adults than "WALL-E" did. The opening few minutes of "UP" was aimed right at adults. I think very few children got it. Many women in the theater were in tears during that first few minutes, including my Wife. The characters drew on many common aspects of good adult relationships making it easy for most people to relate to, at one point or another.