WALL·E is an incredibly sweet film. That's "sweet" as in "Awwwww!" not as in "Dude, that movie was totally frickin' sweet! High five!" I thought I should make that clear. The first thing to do is to realize that the humans are the subplot. Sure, there's something about the future of humanity and some environmental themes, as well as a certain amount of "get outside and exercise", but that's all secondary to the real plot: a love story between two robots. WALL·E is a robot that's gone crazy from centuries of being alone, and he's turned into a romantic. When EVE shows up, it takes him awhile, but he wears down her programming and turns her into a romantic too. When he's let loose on people, he has the same effect on them.
That's why I don't care that much about whether the people are successful at the end of the movie (my guess is that they're not). The important thing is that they have a dream now. But the really important thing is that WALL·E and EVE are together. Awwwww!
Also, the "Presto" short before it might be my favorite Pixar short ever. It's very funny, and it successfully walks the line of having a trickster character (in this case, an adorable bunny) that plays pranks but stays likable and sympathetic.