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.
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, adding gasoline to an already white hot fiery debate, or perhaps dousing 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.
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
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 there is some Ship Sinking along with 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.
Tastes Like Diabetes: For those who didn't like the movie (and even for some who did), the ending was this and for being a very predictable and cliché ending.
They Wasted a Perfectly Good Plot: 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.
Unnecessary Makeover: The brief flashback to a live-action "young" Tootie is certainly more recognizable to the viewer than the live-action "adult" Tootie.