For readers who have already seen one of Miyazaki's films: he is still in top form and made another worthwhile experience. Okay, you don't need to read any further now.
I already guess most readers are older than the two protagonists of this picture, so I should say Ponyo is not so much a family film as a chance to remember the feeling of being a small child: discovering the world as you wanted to see it, making up your own rules and boasting an exuberant enthusiasm at doing things on your own for the first time. Ponyo swerves away from many of the problems that all-age films tackle. It never condescends, all the characters have good genuine hearts and believable problems.
The two main characters may be two of the most believable children I ever saw put on screen. They are not simple minded, arrogant or naive, just curious, enthusiastic and learning the ways of the world. They are so easy to love, but even more easy to identify with. Many films regard children from the outside, as the adult looking into a world only a child could enter. Ponyo brings everyone back to that world. In Ponyo, there lies the first time to learn and choose what you care about most, which the film values with high esteem. It is worth it to remember, to feel it again.