I agree that the story wasn't as great as some of Miyazaki's other works. However, I thought the animation in this film was simply amazing. Especially during the scene Ponyo was riding the waves in order to follow Sosuke.
My wife and i really dug this movie. We'd only watched it once but had a long stretch of singing the theme song at random times afterward. I also fondly recall Tina Fey's occasionally stilted voice acting, and oddball lines, like "i'm worried about the seniors", which even years later, i quoted last week