"Overrated" is subjective, and you really have to have a damn good reason to call something overrated.
I've seen the film, and what I will say is it did exceed my expectations as far as the dialogue writing and the visual creativity of the world, which shows the usual care and research that Disney puts into crafting immersive settings. Their research having studied real animals, cities, and police departments really paid off for the most part. To all of it, however, it's far easier for a Disney or Pixar film to extract praise for the setting and immersion because the bar has been set relatively low by the rest of the animation industry, and there is an obvious and deliberate tinge of familiarity running throughout the whole thing because it's a Disney product specifically made with regards to their heritage. It doesn't discount the hard work, but it shows how much they run rings around their competition.
As for the writing itself, it tells a surprisingly well-balanced variation of the classic "American Dream" story arc. Zootopia isn't the utopia that young, optimistic Judy promised herself it would be. At her lowest point, it seems like hell, but as she matures beyond it, she finds it's neither and she has to learn to make the best out of what things are. The movie makes the point in its dialogue, which is very natural, sharp, and timely.
The only thing I'd consider overrated, IMO, is some of the other dialogue. I personally found much of the metaphor pretty obvious and heavy-handed in parts, but this is a very "your mileage may vary" situation, and it's a hard thing to veil into subtlety without confusing the message. Much of the success of the film comes from timing; it just came out against the right political climate for its message to stick.
The only part of the film I really take issue with is how it negatively portrays Judy's parents talking about "settling" for their lot in life in an incredibly forced and caricatured way, as if to portray people who don't achieve or strive for their dreams as Debbie Downer-esque dream killers or somehow less legitimate than people who do so. A lot of people make a good living and are perfectly happy with settling or going with the flow rather than taking charge. This could have been portrayed better in the film as a looming temptation for Judy to return to the comfort of her previous life but to reject to show just how committed she is to her ideals. It's such a minor part of the film that a lot of people miss, but it would have meant more to me if they would have handled it better.
All in all, I think Zootopia is animated filmmaking at one of the finest degrees it can be in this day and age. I don't like it as much as most mainstream critics, audiences, and especially furries do, and there are a handful of other animated features to have come out since 2010 that I've enjoyed more. But I've outlined what I like more or less about it and I can definitely see what others got out of it more than I did.
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