Well, since I said it was my favorite, I guess it's up to me to defend it.
To me it's like Idiocracy, an indictment of where we're headed as a species that cares more for rampant consumerism than anything else. I totally see that as our future if we're not careful. Though Idiocracy was more about idiots reproducing at a faster rate than intelligent people, I think Wall-E and Idiocracy are inherently related. Consumerism and idiocy are only separated by a matter of degrees. Everything else, I'll assume is outside of the realm of the user guidelines.
I think the characters interaction is beautiful and as touching or more-so as any non-human's quest for humanity as ever depicted.