The debate over the movie casting was so intense that entire forums were divided over it, with those supporting the casting and those against it being banned for their opinions. Protesters considered those who supported the casting as blind and shrugging off a big issue, while those that eagerly anticipated the movie saw the protesters as not 'true' fans.
Firebending only being able to manipulate pre-existing flames (except in special circumstances). People tend to either be upset that it's not the same as in the show, or feel that it now fits with the other three bending types in that it doesn't create the bendable element.
Ensemble Darkhorse: Francis Guinan as Pakku has been noted by several reviewers to be the one actor to escape the film with his dignity intact, putting real effort and emotion into his scant screen time in stark contrast to everyone else. Seychelle Gabriel's performance as Yue also was moderately well received by fans, and Bryan and Mike would later cast her in The Legend of Korra.
Fandom Berserk Button: The movie is this for fans of the original show. Half of the Avatar fanbase refuses to admit that this movie even exists.
When the Earthbender prisoners are staging a revolt, we see six Earthbenders moving in perfect precision and choreography, stomping the earth and releasing a mighty battle cry... and a tiny rock barely bigger than a football floats by very, very slowly. A seventh Earthbender then launches it at a guard. A fan theory suggested that the dancing Earthbenders were actually responsible for making the earth walls previously used to block the fire blasts, but the scene alludes to the cartoon, in which Haru's father was the one who made the earth wall. It probably would have been more effective if all seven benders instead each picked up a moderately sized rock and just threw them.
"The Ember Island Players" episode, which came out at the time when this movie was in production. Needless to say, a lot of jokes were to be had using footage from that episode to showcase how bad the film was. The last line in the episode especially, which has the heroes say the show they just saw was awful but the effects were nice.
Seychelle Gabriel (movie Yue) voicing Asami in The Legend of Korra, a character first intended as a simple Romantic False Lead but was changed to become much more prominent when she became popular with the fans. The hilarity doesn't reach its peak until the end of the show, though, where Asami ended up becoming the titular Korra's final love interest.
Internet Backdraft: Online criticism of the film reached apoplectic levels. Luckily, capital letters and boldface are unlimited resources.
Memetic Mutation: Before the movie had even come out, early test screening reviews mentioned a scene that has turned the phrase "punching the fish" into a meme◊note He actually stabs it with a knife.. Other gems include the pebble dance (the most notorious example of the Flynning mentioned abovenote Six earthbenders. Four seconds of kata. One rock, slightly larger than a human head.), Kat-tackle (Katara pushing over a random guard and then just standing there), Zhao constantly mentioning the secret library, Ozai's glowing ass (from a screenshot in which the source of light appears to be Ozai's rear end), Yue's line about believing in beliefs, and her penis hair (how it looks like when viewed from the back◊.)
The Scrappy: Live!Katara has far fewer fans than her cartoon counterpart, mainly for hardly being like Cartoon!Katara and her actress having a severe case of Dull Surprise. It also doesn't help that this script removed many of her strong Character Development moments and gave most of the rest to Aang.
Ship Tease: The ending of the Oasis fight was significantly more... Zutara-ish.
Snark Bait: Oh, so very much. It's in reviews, it's in forums, and it's in TV Tropes, and it's all because the movie is so awful.
So Bad, It's Good: For all the snark the movie earns, it's good for riffing on at least.
At the beginning, Katara splashes an off-screen Sokka with water, but he is completely dry when he appears.
In what is purportedly an arctic area, you can't see anyone's breath.
At times, the waterbending is not even animated.
The firebending is pretty much nothing but poorly composed live-action fire elements with CG that even the film version of Spawn would reject.
The last-minute 3D conversion was universally panned, and put a severe setback for the idea after the otherAvatar helped forward the technology; Roger Ebert outright said The Last Airbender put the nail in "low-rent" 3D in his very negativenote He gave it half a star out of four, the lowest score he would give a film he didn't consider personally morally offensive. review of this film.
They Changed It, Now It Sucks: Long before the movie was anything more than a casting list and a few trailers, fans were complaining about changes to the source material. One of the biggest examples from the movie once it finally came out was the pronunciation changes, which Shyamalan deliberately included to make the character names sound closer to their "correct" Asian pronunciations (even though most of the names were made up) than the Americanized pronunciations from the cartoon. Fans were not pleased.
The Agony Boothobjects to what its recapper considers a sexist tone in the film, pointing out that a number of important moments for female characters (Katara's speech to the imprisoned earthbenders, Yue realizing she can sacrifice herself to restore waterbending) are given to male characters instead.
Aasif Mandvi as Zhao. Mandvi is a primarily comedic actor best known for his work on The Daily Show. Shockingly enough though, he end up being one of the most faithful characters to the source material.
Many fans of the original cartoon would have preferred Asian actors to play Katara and Sokka because although the characters have ambiguous racial features, their culture is based on Inuits. Caucasian actors Nicola Peltz and Jackson Rathbone were cast instead, but all the Waterbender extras were Asian or Inuit actors, so the main characters don't seem to belong to their own tribe.