My two year old loves this book and often asks for "Stanley Fish" whilst thrusting the book into my hands to read to him. He also likes to join in when Stanley exclaims "Jumping Jellyfish!" at certain times in the story.
We originally borrowed this book from the local library and ended up buying a copy, because my son enjoyed it so much.
My only negative point is that some of the text is printed on quite a dark background, which makes it a little more difficult to see.