I absolutely LOVED this movie, and - as you know - I'm not the only one. XD
But there's a reason for it's popularity; it has an amazing storyline with amazing characters! :D
I found this essay written by Michael-GoldenHeart (https://www.deviantart.com/michael-goldenheart) who really went in depth with the characters and the plot. His review is really well done and there's not much more I can add to it so I invite you to go check it out!
I also watched a few Youtube reviews about it and looked at a few comments. Some people explained the meaning behind the movie really well and I couldn't do much better, which is why I'd like to quote them.
(these are comments taken from this video: