Like Maxie, I really liked the smooth, solid CGI animation in the film. Visually, it wouldn't look out of place in a Pixar or Dreamworks movie.
The story and writing, however, leaves a lot to be desired. It seems like they just mashed a bunch of semi-funny jokes together, put boring conversations between them, put a plot behind them, and stretched it out to 90-minutes.
None of the characters were likeable, really, with the slight exception of that cute WALL-E clone (forgot the name) that has the most personality out of all the characters in the film.
I did chuckle a bit from time to time. But for the most part, Planet 51 just isn't my cup of tea.
Rating: C-