I'm sorry, but it is the one of the worst Studio Ghibli movies I've seen. Right from the characters to the plot, everything is weak.
The plot is of a weird-looking fish with chicken legs, wanting to be human, and who would do anything, like even induce a tsunami to fulfill her wish by opening some magic well which brings the moon closer to the earth and threatens humankind by drowning it in sea water. Now, the only way to stop this turmoil is asking a five-year old boy to promise to love this girl/fish till he dies (not creepy at all) and the world is restored to normal.
Something about the characters:
Sosuke - A five-year old boy who thinks he is attaining greatness by promising to love a fish.
Ponyo - An annoying, stubborn fish that wants to be human and is made to look cute by squirting water on others, yelling 'Ham!' every few minutes, and constantly falling asleep.
Lisa - Sosuke's mother who used to roll with Dominic Toretto's crew.
Fujimoto - Ponyo's father who is portrayed as the antagonist, but in fact is the only one who actually cared about that not-so-cute fish.
Gran Mamare - Ponyo's mother whose only job was to ask Sosuke if he will love that fish at the end of the movie.
That's it! I know it's a children's movie, and I'm not asking for Interstellar or Inception like plots, but if the same studio is giving me Princess Mononoke, then, yes, my expectations will be high.