'Planet 51' was the last thing showing at our local theatre that I hadn't already seen. The previews and lobby displays (mis)led me to believe it was just another throwaway kids' cartoon, full of forced cuteness, predictable gags, and cardboard characters; but I had time to kill and the ticket was at matinee price, so I finally went in. Am I ever glad I did!
The obvious send-up of 1950s American culture is fun, and so is the shoe-on-the-other-foot twist of the human being viewed as the fearful alien menace, but if that's all a viewer takes away, he or she is missing a lot. There was plenty of unexpected satire that had me laughing out loud through much of the film. There is also a profound message that centering one's society around perpetual fear can cause more harm to a culture's core values than the thing being feared; however, the message very carefully doesn't get in the way of the humanity (alienity?) of the story.
The music was well done and really enhanced the fun. Visually, I loved the film. Character design wasn't anything particularly special, but the look of the planet itself was gorgeous. This is a cartoon, after all, not an overblown CGI extravanganza like Avatar, so you shouldn't expect photorealistic rendering of every tiny detail. The beauty of this kind of artwork is in the imaginative forms and colors, the simplicity of shapes and lines that enhance the story, not overwhelm it.
Actually, having brought the subject up, I suppose many comparisons and contrasts could be drawn that make Planet 51 a kind of Anti-Avatar. Here, the humans are neither conquering villains, nor paternalistic hero figures. People--er, beings--from both sides have to do their part on Planet 51 to bridge the misunderstanding of cultures and enable goodwill to prevail. That may not be the kind of dramatic plot it takes to engage some viewers' attention these days, yet it's exactly the sort of solid but gentle storytelling one should expect from the offspring of George Harrison's Handmade Films.
Plus, so far as I can tell, no one has yet suffered depression after viewing Planet 51. :)