These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Others have argued that the message itself is actually subtle when compared to other Green Aesops - or at least it was for the time.
And An Aesop that went overlooked was the fate of the town in the TV Special - once the Truffula trees were gone, they picked up and moved to brighter pastures, as any Ghost Town in the Western USnote Established during the Gold Rush in the 1800s can attest to being Truth in Television.
Strawman Has a Point: In the TV special, the Once-Ler says that he can't just shut down the plant and lay off ten thousand workers because it's bad for the country. Even the Lorax admits he has a point here.
Straw Character: The "nature" depicted has no bugs, parasites, diseases, dangerous animals or anything "icky" about it like any real wilderness, it's completely an unrealistically ideal portrait of nature. Also, it fails to account for the fact that businesses have a bona fide profit motivation to protect the wilderness, at least the part of it they're using (if the Once-ler had been smart with his business plans they would have included replanting trees, it's just common sense). He's the Once-ler because his strategy is good if you're amoral and only care about making money once (rather than continuously).
Not using up whole forested regions (and animal/bird/fish species), until they are completely exhausted as a useable resource, then switching to a lower-quality or harder-to-access resources was a rather unorthodox thought at the time of the book's writing. And if you think such practices are a thing of the past now, think again.
Tear Jerker: Any of the reprises played during the exoduses of the Barbaloots, Swamy-swams, Hummingfish and Once-Lers. Also the song Once-Ler sings when he's analyzing himself, guilty of what he's done and personally ashamed to be a Once-Ler.
Crossover Ship: The Once-ler seems to have become the patron saint of this trope. Go to any movie's YMMV page that lists crossover ships, and it will likely list the Once-ler paired with whoever's in the movie.
Ear Worm: "How Bad Can I Be?" and "Let It Grow (Celebrate The World)".
"Thneedville" should also come to mind.
Ensemble Darkhorse: Once-ler is pretty popular as it is, but evil Once-ler was only on screen for a few minutes (his Villain Song and the scene that followed it) and yet he's gotten a ton of fanart.
Estrogen Brigade: Younger Once-ler attracts A LOT of this. To the point that he has become a fandom of his own.
Fanon: In the case of Ted's mom, some have christened her as "Helen", named after Dr. Seuss' first wife, as in a similar fashion how Ted and Audrey's names were based off of.
The Once-ler's mother's name being Isabella. But the funny thing is, nobody knows how that name came to be or where it even came from but many decided to use it when referring to her in fanfics or in general.
Fix Fic: The amount of time devoted to things that weren't part of the source material, the way a large portion of the original story was abridged into a single song sequence, and the fully resolved happy ending in place of a thought-provoking question-mark ending make it like one to an extent.
"Funny Aneurysm" Moment: All those cute scenes of the Once-ler interacting with the animals are considerably less heartwarming knowing what he ends up doing to all of them.
Hilarious in Hindsight: Those Misaimed Marketing deals down below that make the Lorax into a product mascot? The film mirrors this in one scene where the paparazzi takes a photo of the Lorax accidentally holding a Thneed, then posting on an ad now claiming Thneeds are "Lorax approved".
Also promoting the movie is the typical host of theater paraphernalia... including putting the film's logo on disposable paper popcorn holders. Again, it does not take a genius to ascertain why this runs somewhat counter to the message of The Lorax.
Universal is treating this film like any other major Hollywood animated blockbuster, by giving it 70+ tie-ins with products, immense marketing strategies, and celebrity voices. What most people don't seem to get is that the message of the book is that it's WRONG to buy into excessive "Thneeds" that harm the environment!
In general, the kids are sucked in towards the cute animals, despite the fact that they appear only in flashbacks and are evicted out due to destruction of their habitat.
Misblamed: A number of viewers and critics accused the Lorax of trying to kill Once-ler by sending him afloat the river on his bed...despite the fact that it was a freak accident from a sleeping Once-ler that put his life in jeopardy (his leg accidentally steers the bed down the wrong stream, toward a waterfall), and the Lorax outright says after he saves Once-ler that he didn't want him dead, just to "harmlessly drift away downstream". If he had really wanted Once-Ler dead, he probably wouldn't have used a pair of bar-ba-loots as a Magical Defibrillator.
Old Man Once-ler when he's first seen peering through the window and reaching out at Ted, but he just gets less scary from there.
Also, "How Bad Can I Be" is pretty fun and upbeat for a Villain Song...until the very end, which has a giant Once-ler looming over the entire forest which he is destroying, giving a Slasher Smile after shouting the last lyrics "HOW BAD COULD THIS POSSIBLY BEEEEEE?"
Once-ler: WHO CARES IF A FEW TREES ARE DYING?
If you think that's scary, listen to its Dark Reprise, Biggering (complete with storyboard to tickle your imagination). There was a reason it was cut from the film.
Once-ler: "'Who cares if a few THINGS are dying? I DON'T WANT TO HEAR YOUR CRYING!'"
Romantic Plot Tumor: Some find the Ted and Audrey subplot as this. Ted's character development that eventually made him actually care about trees however, seemed to make some people forget about his original motivations in finding a real tree in the first place, so this is somewhat zig-zagged.
The Scrappy: O'Hare to some, both for being an unnecessary addition to the story and for being such a one-dimensional villain. Also, his design falls a bit into the Uncanny Valley. If this film was going to have a villain, couldn't it be one with charisma?
Tastes Like Diabetes: Its more "lighthearted" moments which are subjected to overly cheerful song and dance numbers are this, most likely in the very beginning and very end. Its bright, colorful visuals don't help either. And completely caramelized when little 3-year old Marie suddenly started singing.
They Wasted a Perfectly Good Character: Characters, plural. The Oncler's family actually made far more interesting villains then O'Hare being naturally un-supportive, greedy, and manipulative. Wouldn't it have been better for more of the conflict to show them how bad destroying nature is a bad thing and along the way, maybe reconcile with his family?
Maybe the Once-Ler could have told his greedy family that harvesting Truffula leaves by clearing cutting the forest is as ridiculously self-destructive a business practice as an apple farmer harvesting by chopping down his orchard. Or if he just planted as many seeds as trees he cut down this would have never happened.
Or the fact he didn't set his entire business around a single product from a limited resource.
The Point of the Original was to say that the Once-ler was only interested in making a profit once, teaching viewers a lesson about renewable resources.
It was kind of painstakingly obvious that if you cut down all trees without planting new seeds, no more profit, which is just Stupid Evil from Once-ler's family's part, and Once-Ler's Extreme Doormat preventing him from saying anything about it. The film makers probably didn't want to make it so Anvilcious and avoid Viewers Are Morons, letting logic thinking do its work.
Another Example is the aforementioned Mis-blamed. If the Lorax wanted the Once-ler to float harmlessly down the stream, he should have placed him further down the stream, away from the waterfall turnoff, so there wouldn't be the possibility of him turning down into danger. The turnoff wasn't that far away from where he was placed, and a large roaring waterfall is hard to miss.