Accidental Nightmare Fuel: Hugh J. Magnate's creepily smiling and giggling evil rabbit. Even though it was likely meant as a comical joke, it still manages to be this due to the high pitched laughter and human face on it, not to mention it came right out of nowhere, with only Magnate's Evil Laugh probably hinting at it.
Ass Pull: The Timmy Turner Loophole. Basically, it was created so that Timmy would be allowed to keep his Fairy Godparents even after growing up. Even if it was justified in that Fairy World does owe Timmy big time for saving them on more than one occasion, it still came out of left field and undermined the point of the special, which was to have Timmy grow up.
Cosmo and Wanda's CG designs. Some don't mind them (especially since they were more or less high-definition versions of the models from the Jimmy Timmy Power Hour), but others would've preferred them done in the show's old style, or anything if they flat-out hate the CG.
Tootie's adult casting and characterization has torn up the fanbases, especially Tootie fans. Some find it a good way to show how she has changed and matured since she was a child, as well as providing a reason why Timmy would be into Tootie, while others thought it made no sense for her to move past her stalker tendencies and become a normal popular girl, making her more shallow because of this drastic shift.
Some fans won't acknowledge it. Aside from perceived quality, a common reason is that it contradicts the Distant Finale of Channel Chasers, which shows Timmy indeed maturing and growing up while living a normal life. To fans satisfied with that ending, this comes off as a Happy Ending Override. This ended up being mitigated as it was revealed it was an Alternate Continuity in the first place considering later seasons of the show would contradict how this movie would even happen in the first place (Poof eventually growing older and going off on his own, Chloe and the whole fairy share deal, etc).
Even for those who otherwise like the movie, the third movie did not happen.
First Installment Wins: While it's no masterpiece, fans tend to hold the first movie in the highest regard.
Harsher in Hindsight: Drake Bell was found guilty of an incident involving a minor. Timmy being played by Drake Bell, the overall theme of growing up with Bell staying a kid, him being friends with some of Crocker's students (who are children, by the way), and especially this promo for the film where Timmy wishes he was Drake Bell just look uncomfortable now.
Just Here for Godzilla: Quite a few viewers just watch this film for David Lewis's take on Crocker, feeling he brings plenty of energy to the role compared to everyone else.
Memetic Mutation: "I wish... I wish I was Drake Bell!" Explanation In one of the promos for the movie, a cartoon Timmy wishes he was Drake Bell. After Drake was found guilty for sex crimes involving a 15-year-old in 2021, the clip of Timmy wishing he was Drake started making rounds on the internet, except edited to where the result of the wish is an adult Timmy from "The Big Problem" being put in prison, Drake being found guilty during his trial, or him being chased by the police.
One-Scene Wonder: Jason Alexander and Cheryl Hines as human Cosmo and Wanda, much to the disappointment of many who felt they were much better than the CGI fairies with their TV voices that were used through most of the film.
Questionable Casting: Most glaringly casting Daniella Monet to play a conventionally attractive, glasses-less, adult Tootie.
A character match-up quiz on the official Nickelodeon website strongly suggests that Tootie was the mystery mother of Timmy's children at the end of "Channel Chasers", which either added gasoline to an already white hot fiery debate or doused it with a splash of cold water, although some people just prefer not to think of this movie as the real ending to the series, as well as not taking the quiz seriously since this isn't Butch Hartman himself saying it.
So Okay, It's Average: The general consensus for the movie. While it's no masterpiece, it's not the utter trainwreck people expected it to be.
Squick: A twenty-three year old man acting like a child, even if it is an act to keep beloved fairy godparents is kind of creepy. It becomes even more creepy when you realize that this Manchild is likely sharing a locker room and bathrooms with other ten year old boys, and even moreso when Drake Bell was found guilty of sex crimes involving a 15-year-old.
Tainted by the Preview: There are fans who really dislike the idea of making a traditional Thick-Line Animation series into a Live-Action Adaptation. The few previews that were shown prior to the movie's premiere did little to alleviate those fans' doubts about this project. There are a variety of reasons for this ranging from Avatar: The Last Airbender's live action movie (perceived by people to have been done very poorly) to the fact that Timmy Turner never grew up and is now a creepy Manchild. Even though the movie has now aired, the reaction still is mixed about it.
Timmy being forced to make a difficult decision between finally growing up with the love of his life or continue to live the way he is with the family he loves so much? Sounds like it could have made the perfect finale for the series. But alas, that is not the case.
Alternatively, the idea of Timmy growing up and all the resulting drama could've been set during Timmy's high school years, which would also have been more relatable to the very fans who grew up with the show itself.
As the movie's Big Bad is a greedy, rich yet comedic tycoon that's made up for this movie, some fans were confused as to why the film didn't just use the character from the show who already fit that bill, Doug Dimmadome.
Unnecessary Makeover: The brief flashback to a live-action "young" Tootie is certainly more recognizable to the viewer than the live-action "adult" Tootie, and while Daniella Monet is a pretty woman, her character loses Tootie's adorkable appeal and becomes a more generic love interest.
. Timmy being played by Drake Bell, the overall theme of growing up with Bell staying a kid, him being friends with some of Crocker's students (who are children, by the way), and especially this promo