Okay I saw this with my little brother a few days ago. And actually watching the series when I was younger I was pretty disgusted by this
It's 8% on rotten tomatoes and hatred by most major movie critics speaks for itself but I still feel like bitching.

They pulled plots out of nowhere, changed good plots that set a lot of things for the story around and just made them pointless. An example would be is when Aang is captured by the fire nation. That occurs in a forest and he is taken to a fire nation military base. In the movie however, he is taken in a temple that was shown early on in the series and then held at the same temple. If that isn't bad enough another example would be them adding the little scene at the end where the comet that an old Fire Lord used to kill the airbenders was said to be due in three years, while in the series, it takes Aang a full year from when he gets out of the iceberg, to when he defeats the Fire Lord

They also jumped between major plot points in the series at a rate that was both quick, and didn't allow for any actual plot for the movie to develop. They basically (well rather they did) took the first oppertunity to just directly say "We're going to get people to teach you this stuff then your gonna kick this guys ass"

and at the end they said that the comet was due in three years while the series only took a year for Aang to get out of the iceberg and defeat The Firelord.

So combined with horrible dialogue, shitty actors and casting, and a gross destruction of the the series story. I think that The Last Airbender should go like the Eragon movie did.
Die with the first movie and not have any sequels made.
That is, unless they hand the job to a more talented director who fires the entire cast and then treats it as though the first movie didn't exist and makes up for it with an exceptional second movie.