This post includes complete, fun-negating spoilers. Do not read if you haven't seen Wall-E yet!
The first two thirds of Wall-E (until the Captain starts talking) is amazingly great. Pixar's greatest work, including the Incredibles. They have effectively a silent movie with a robot on a destroyed, garbage-filled Earth that is compassionate, warm, and endearing. Before Wall-E, Lucas owned robots. Wall-E makes R2 look like a 8-bit hack. His bazillion-points-of-articulation eyes, insanely clever physical design, and his collection, organization, and adoration of unique human garbage makes him brilliant. Pixar excels here because I believe robot humor is all about making you think the robot is a human, then doing something unexpected to remind you it's not. Pixar's creativity shines brightly through constant surprises. The first 2/3rds played out beautifully because they relied on the roots of Chaplin movies; an instantly beloved protagonist and inventive physical comedy.
My problem with the last third (it may have been shorter than that but it seemed to go on forever) is that much of the lightness and artistry of the first two thirds is trashed through clumsy Pixar-rhetoric dialog by the captain and the jabs at modern human society going from subtle to street-corner preachy. The giant (30 minute plus?) chase scene was a soul-sucking endeavor that lacked much of the creativity that the rest of the movie exhibited. (Monsters Inc. is the textbook example on how to do a final chase scene.) The crazy robot ward was a highlight, until they went from the loony-bin to the wacky off-beat mascots featured in nearly every animated movie. The final scene of bringing Wall-E back to life might have not been completely cheesy had the last half-hour not sapped all my suspension of disbelief.
Few things are more vexing than something that is mostly magnificent but partially crap. Wall-E could have been Pixar's best movie had they never set foot on the human spaceship.