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.
YMMV: The Last Airbender
Awesome Music: James Newton Howard's score is quite possibly the best thing in the entire film.
Zuko. He goes from the angsty but determined powerhouse in Season 1 and turns into a whiny, Pirates Who Don't Do Anything type. His Crowning Moment Of Awesome from Season 1, defeating rival Admiral Zhao and proving his worth as a Firebender, is instead given to a handful of random Waterbenders.
The Fire Nation in general. Firebenders can only manipulate preexisting flames. Sozin's Comet, which previously allowed Firebenders to wipe out entire civilizations in a day, now apparently only makes all Firebenders roughly equivalent to a normal, non-cometed Firebender in the series.
Zhao finds more time relying on the Fire Lord (and the scroll from the great library) rather than be ambitious and power-hungry.
Fire Lord Ozai is also less menacing than his animated counterpart.
While not a Badass until the end of Season 1, Katara underwent this via Chickification.
Sokka doesn't resemble his more serious and sarcastic Book 1 self.
Broken Base: 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.
Ensemble Darkhorse: Dev Patel, Shaun Toub, and Aasif Mandvi's performances as Zuko, Iroh, and Zhao were considered the best performances.
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. Also, the fight scenes are all shot with a single camera, with no jump cuts. This leads to the problem of showing the audience a large number of mooks standing in the background, not doing anything while their friends are getting knocked senseless. It probably would have been more effective if all 7 benders instead each picked up a moderately sized rock and just threw them.
Hilarious in Hindsight: "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 this film was.
Internet Backdraft: Online criticism of the film reached apoplectic levels. It's a good thing that capital letters and boldface are unlimited resources.
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◊.)
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 than the Americanized pronunciations from the cartoon. Fans were not pleased.
The Scrappy: Katara has far less 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 many of her strong character development moments were either given to Aang or just removed entirely.
Many fans of the show thought that it was racist to change the hero/villain dynamic from Eurasian-looking, blue-eyed Inuits versus evil Southeast Asians to heroic Caucasians versus evil South Asians and Polynesians.
Aasif Mandvi as Zhao. Mandvi is a comedic actor best known for his work on The Daily Show.
Many fans of the original cartoon 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.