The whole idea of the story is to never lose who you are, and that it's okay to cry when you feel hurt. At first, her emotions went haywire. While to children it would seem like the emotions were bickering, the actual meaning was that Riley felt confused and a whole bunch of emotions at once. Then, when the islands began to fall, it was showing that she was losing who she was. She was so angry, scared, sad, etc. that she lost sight of her friends, family, honesty- she lost who she was. Then, when Sadness took over in the end, it showed that it's okay to cry. Sometimes you need to call out for help in a way everyone will understand- Sadness. It was pretty mature for a kid's movie.

I do hope they make a Squel to it