"Ponyo" takes concepts from The Little Mermaid (original, not Disney), some of Miyazaki's other movies, and apparently a Japanese folk tale or something like that. For instance, like The Little Mermaid, it is said that Ponyo will "turn into sea foam" if the human boy doesn't really love her. Anyway, the point is, this movie was verrrry cutesy, and a little more directed towards children than films like "Howl's Moving Castle" or "Spirited Away." I was kind of embarrassed to be the only adult in the theater without small children with me.
The English dubs are ok, slightly annoying but definitely not the worst I have seen. The plot was pretty decent but some aspects of it just felt a little overdone. Certain characters, like Ponyo's father, were reminiscent or characters from earlier Miyazaki films. Be warned: it is sugary sweet. I would say that "Ponyo" is worth a rental or something - unless you want to take your children with you (or borrow someone else's.)