Saw a packed midnight show last night and went with several friends, not as many as originally planned but at least I was there with a bunch a fans in the audience. Cosplay, lots of ATLA and TLA shirts, overall a fun outing with people that love the show and wanted to love the movie.
I think its the casual fans (besides professional critics) who are most upset by this movie. They're the ones sitting behind me going "Ong?" Because real fans would have known months in advance of these changes

I guess we're die hard fans on here

Because the shock and awe and complete silence throughout the movie was often interrupted by me and one of my friends totally enjoying it at times. And if you're a fan you will enjoy moments but you may not enjoy the movie as whole, because everything you've heard or read by now is true with one thing missing, and that is that you'll just have to see it for yourself. Personally, I separated this movie from the show completely as I mentally prepared myself the entire day for my midnight show. This in part due to all the negative reviews.
As a fan, it was hard for me to feel hatred towards TLA, and I agree the reviews are excessively harsh, but even if they lightened up just a bit I don't think it would help. Quite simply the movie was flawed and full of holes. It was rushed, the writing was bad, that bad writing then leads to actors delivering bad lines, there was zero room for character development or even time to absorb the wonderful world they're in. It was heartbreaking to watch (just as others have said) at times because everything going in looked so good with only a few red flags along the way as we followed the production of this movie for almost two years.
So I'll start with the nail in the coffin. Running time! I know I'm just repeating myself but finally after seeing the movie, there was so much information and details that needed to be
shown rather than explained by characters that it absolutely needed or probably contained 30 minutes of footage that was not there for the audience to comprehend going from one scene to the next. Katara's narration was a cop out. A post production tool used to move the story forward as scenes that were filmed now became a montage of sorts about their journey to the NWT. And that really hurt. Because the movie starts off faithful and then slowly becomes a collage of scenes taken directly from the show to live action.
M. Night is usually good at building suspense and playing up the drama to emotional climaxes. It is the first time in all of his films that I did not feel it. His strong point here was attention to detail and visuals, just about everything from the sets, to costumes, and special fx for the bending are all quite stunning. It truly was A:TLA brought to life. Unfortunately, the film felt lifeless, and it is because of how much is thrown at you all at once. I just wanted them to slow it down and let the audience breath and get to know the characters. We know who the characters are but even in this movie they felt like strangers.
But don't let me bring you down just yet, because the next thing I will say is that this was a movie made for the fans, with a few known exceptions and changes of course. Or at least Night really tried to make this for the fans, because there were things in the movie that made me want to thank him personally and other moments that left me shruggin my shoulders. There were absolutely moments where it really is the show coming to life. And maybe that's where he lost the critics, this attempt at being very faithful. And it was also in this attempt to be too faithful that he lost all those casual fans and even us die hard fans. Because he basically forgot he was also supposed to be making a good movie that more than just kids and fans can enjoy. Somebody mentioned the movie has a charm to it, and this is very true, but it fell short on way too many standard do's and dont's of storytelling and filmmaking.
So now let me get all list-y on you just to wrap it up in case you weren't ready to read my book.
The Good:SFX, Sets, Costumes, Cinematography, Film Locations! All of it was visually stunning!
James Newton Howard's score was beautiful as we all knew by now
Dev Patel as Zuko was awesome.
Believe it or not...Jackson Rathbone as Sokka! Not hilarious the whole way through but he was great.
Noah Ringer was awkward at times but he held the film together. And for his first film I mean c'mon, hats off to him
Shaun Toub was underused but still passable as Uncle Iroh so no complaints.
Yue was surprising good and came across very natural.
Pakku, even though they only mentioned his name once I think was good but underused as well.
The action was good and comes and goes but Night needs to work on it but it still gets a pass because the more they showed the more you wanted.
Appa and Momo looked fine but were underused.
Specific scenes like the Blue Spirit and Aang vs. Zuko were some highlights for me.
Neutral:Aasif Mandvi as Zhao was up and down, sometimes perfect and other times just not the right guy for the part.
Cliff Curtis did what he could with what little he had to work with. If they only showed his face just once it would have been more effective. He mostly just seemed like a rich guy with a lot of power who has people report to him without consequence of failure. Unless we're talking about Zuko.
The cliffhanger ending would have worked great if Night had truly won fans over.
Spirit world, nothing special.
Live action opening of the shows opening introducing the elements.
Sins of Shyamalan
Name changes backfired, don't ask just ask my entire theater. Even saying "grandma" instead of Gran Gran.
Nicola Peltz as Katara.
No interaction between Aang and Appa.
A Dragon replacing Roku and Koh
Cutting the Kyoshi Warriors...I now know after seeing the Last Airbender Revealed that it was M. Night's decision.
Using Dee Bradley Baker should have been a no brainer for Appa and Momo.
Exposition Overload! Katara Narrating and conversations between Ozai and Zhao.
I'm not mad about Koizilla being cut, I'm mad that the tidal wave was not as epic and as powerful as it should have been.
Not making Iroh's scene cool enough! In the show he threatens Zhao and warns him not to kill the moon spirit, and then unleashes the fury...but in the movie he just creates fire

There was no real build up to Firebender's fearing someone who can create their own fire so I don't know why they all just cowered before him, I mean we're supposed to be waiting for Iroh to do something truly bad ass and that should have been it. A zuko vs. Zhao fight would have been great as well.
In conclusion, because I dare not let this drag along...I do not think the movie will reach the box office heights needed to warrant Book2 and the reaction from critics and fans alike...I don't know, I don't think there's any recovering from this and why would people want to see a sequel to a failed first attempt even if the story is better in season 2, and we get more money and a longer movie.
I honestly think that Night should have hired Mike and Bryan to write the screenplay collaboratively with him. Anybody but him. He had his chance to really redeem himself with this film but something a long the way was lost. He was either in over his head or the studio execs and producer's really did twist his arm. I would love a director's cut, and I have no problem placing a TLA bluray right next to my ATLA box sets. I didn't hate it, I'm disappointed but I didn't hate it and I don't hate M. Night. I think the feeling now that we may never get our next two movies is the only thing that hurts in the long run. Our expectations blinded us. I got caught up in the hype but I don't think it was a waste of time. And neither should you.