It's still the only movie my 3-yr-old daughter will sit through. The first 30 minutes is some of the best storytelling ever put to film, IMHO. So much told with so little.
Other Pixar movies like Monsters, Inc. or Cars are either too scary or too talky. Wall-E is the perfect balance, and such a well told story that I never tire of it, either.
It's just more of an adult / documentary thing IMHO. They spent way too much trying to make some principled point rather than entertain. Same with 'Up'. I think perhaps they were catering to people who nominate Oscars or something.
My kids were bored. Gimmie Princess and the frog, Hercules, Aladdin, Little Mermaid etc etc any day.