It takes only one look at the rigid, rubbery aliens in this sci-fi spoof to know that we aren't dealing with topflight computer animation here. But Planet 51 still delivers a few pleasant surprises, including a smart story — a reverse-E.T. riff that plops an American astronaut down in a world of just-like-us-only-green creatures — and clever characters, like a lovable NASA rover with canine programming. He's no WALL·E, but you'd have to be an alien yourself not to smile when he starts wagging his antenna like a robot beagle.
