The story was an allegory for Fascism, corporatism and capitalism, but many perceived it as one for abortion.
It works as an allegory for Isolationist foreign policy too.
Misaimed Fandom: Because the story's Aesop asserts the universal worth of people, even the seemingly insignificant, the book became very popular among the pro-life movement and some believe it's about being pro-lifenote This probably isn't helped by Horton also starring in a book about dutifully hatching an egg, despite the official meaning (as per Dr. Seuss' wife) being about fascism, corporatism and capitalism and the fact that Dr. Seuss himself was pro-choice.
Some pro-life activists think this book was anti-abortion. Not only was Dr. Seuss pro-choice but the book was published two decades before Roe v. Wade. According to his wife, the central allegory is about fascism, corporatism and capitalism — "a person's a person, no matter how small" refers to big shot governments and businesses stepping on the common worker. At one point a pro-life group actually tried to use the line as their slogan, until Mrs. Geisel sued them.
It's also an allegory for how the Japanese were being treated after WWII; the book is even dedicated to a Japanese friend, Mitsugi Nakamura. There's shades of The Atoner here, as during the war Seuss did his share of anti-Japanese propaganda cartoons which he came to deeply regret.
Alternative Character Interpretation: Did Sour Kangaroo really just consider sacrificing her own son just to order an ignorant genocide on Horton's friends? Or did she immediately decide against it and just pretend to consider it?
Awesome Art: The visual development team went to great lengths to recreate Seuss's drawing style for CGI and it really shows, from the rubbery characters to the oddly-proportioned buildings with inexplicable wrinkles on them, to the various nods to Seuss's entire body of work.
"Into Whooville," which transitions seamlessly from symphonic music to a bizarre mix of mambo and South Asian. Good luck getting it out of your head, especially since a loop of it is used for the DVD menu music.
"Mountain Chase." The temp track for the sequence was "The Ecstasy of Gold", and you can definitely tell the influence. It can easily be mistaken for something Morricone himself wrote.
For some, Horton's Adaptation Personality Change makes him this. While Jim Carrey's performance was praised, applying a lot of his signature zany traits to someone like Horton didn't really make a good combination. One animator even not-so-affectionately referred to him as "that drunk guy at a party with a lampshade on his head who's trying way too hard to make people laugh."
Similarly Jane/Sour Kangaroo is either a funny insecure antagonist that proves to have a noble side in the end, or an unlikeable Karma Houdini. This is especially the case for her more extremist 2008 movie incarnation.
The reveal at the end that the Jungle of Nool (and Earth as a whole) is just one speck, like Whoville, among numerous others, floating in outer space.
When JoJo is revealed to have a wonderful singing voice.
What's become of life in Whooville after the Whos find a new home on the clover in the montain in the jungle of Nool?
Franchise Original Sin: The film's creative team relate Sour Kangaroo's Easily Forgiven status to the original book, stating Seuss was not a comeuppance writer. While this was true to some degree (Seuss did punish some of his most unlikeable characters when repenting or enabling them did not benefit the story's message, including Horton's twoprevious antagonists), the book's Sour Kangaroo, while still a Jerkass, committed far less atrocities and changed her ways as soon as Horton was vindicated, while the film's Sour Kangaroo comes off more as a Played for LaughsHate Sink, making her HeelFace Turn seem more dubious.
In Katie's clover world, everyone is a pony and they all eat rainbows and poop butterflies. One episode of My Little Pony: Friendship Is Magic has the cloudcuckoolander Pinkie Pie attempt to eat a rainbow. However, the show did not feature lepidopteran defecation of any sort in its near decade-long run.
All the Whos live in a Small, Secluded World that can only communicate to the outside through limited means. The Mayor's wife, Sally O'Malley, who's voiced by Amy Poehler, says that she doesn't know the feeling of being watched by a giant elephant. Seven years later...
So Okay, It's Average: While not regarded to be an amazing film, it is generally agreed that it isn't anywhere near as bad as the previous Dr. Seuss film, with many seeing it as an alright kids film that is for the most part, true to the original book.
They Wasted a Perfectly Good Character: Dr. LaRue. She appears in exactly three scenes in the movie, and there's nothing much of her character development. This despite the fact that, until Vlad dropped the clover into the clover field, she was the only other Who besides the Mayor to understand the truth about their world. She notably doesn't even come to the Mayor's defense when he's being mocked for his claims.