Yes, it is like CalculatedChaos said!

Still, it's hard to believe that a robot-like character in 1,5 hours can produce the same impression as a human person like Lisa during many many wonderful episodes.
Well, you have not seen the movie - I give the great minds from Pixar-Animation more skill than the Simpsons creators.
But you might be right, they are not meant to be compared, Lisa and Wall-E, but they are meant to be my favorite imaginary characters of all time.
By the way, Wall-E´s mate is
Eva - she is not much of a deep character... but she is so vivacious like my own creation LunaStarshine and that is also a plus why I love this movie so much.