Of course we all know why, morally, The Last Airbender (the live-action movie remake of the first season of Avatar: The Last Airbender) had to fail. If you don't, look up "racebending"; the controversy has been covered well enough by others. (Remember, morality is always entirely about action; beliefs only matter insofar as they (poorly) predict action. It doesn't matter whether Shyamalan and the rest of his crew had racist intent; the casting choices were immoral.)
But even if Shyamalan had cast actors of the right ethnicities, I still skip watching The Last Airbender, and the reviews are proving me right. Here's why it was always doomed to suck:
1) Avatar is complex: A movie adaptation of a long, complex work, such as a novel or TV series, has to boil it down to its core elements. The problem is that the core elements of Avatar are hoary old cliches and the possibly the most formulaic of all stories, the monomyth: As prophesied, a child sets forth on a journey to master his power and become a man. The forces of evil try to stop him while he is still young and weak. Eventually he masters his powers and stomps out evil, ushering in a new age. Exciting the first time you encounter it, but it gets old fast, unless you have something other than plot to chew on -- which nine times out of ten, means characterization.
There's a lot of ways to make that twist. Avatar did it by making the hero NOT the sole focus of the story. Ultimately, it's an ensemble piece, and as much or more attention is paid to developing the characters of Sokka, Katara, and especially Zuko as to developing Aang. But pretty much all of that happens in side stories. Characters aren't solely or even primarily defined by how they interact with Aang, the way they would be in a typical monomyth (see Tengen Toppa Gurren Lagann for example, where every character is defined by the role they play in Simon's story). Much of the character development happens while Aang isn't around, especially for Zuko. This presents a major problem if you're trying to boil nine hours of television down to 100 minutes of movie, because you either have to cut those side stories, losing all that characterization, or compress the side stories until they're so short that you lose the characterization anyway.
Of course, there's the third option of heavily rewriting the story so that the characterization is merged into the main plotline, but the level of changes needed to that to Avatar crosses the line from "adaption of" to "loosely inspired by."
2) Hollywood: Hollywood loves the monomyth. Hollywood is obsessed with the monomyth. Producers who have never studied literature outside of one required course in college will, upon hearing a pitch, ask about the Call to Action, the Road of Trials, the Temptress. The problem is that they don't understand that the monomyth is an analytical tool, not a formula for writing stories. Hollywood will always pull a story closer to the monomyth if they can -- and Avatar is pretty close to the monomyth already.
Even the most well-meaning director, who understands the craft storytelling deeply enough to know better, will still face pressure from his financial backers to follow the formula. And if the story is already almost at the formula, pulling it closer still, coupled with paring it down to series length, is going to produce an insufferably formulaic movie.
3) Shyamalan: Seriously, how does this guy keep getting backing? Every movie he's made is worse than the last -- Sixth Sense was good, albeit shallower than it thought it was; Unbreakable was decent; Signs was unmitigated crap. I haven't watched his movies after that, but broad consensus is that they're terrible.
I've seen reviews of The Last Airbender comparing him to Ed Wood and Uwe Boll. That level of awful is practically an achievement in itself.
4) Live Action, Realism, and Grit: Avatar was heavily inspired by the works of the greatest animator of all time, Hayao Miyazaki. The series is heavy on gorgeous, highly detailed scenes of natural beauty, with just a touch of the surreal and the impressionistic. Often times these aren't tracking or establishing shots, but backdrops on which the action unfolds, noticeable only on repeat viewings. Certainly a live action movie is capable of such beauty -- the Lord of the Rings movies pulled it off, for example -- but the tendency when adapting animation is to make it more "realistic", and as we all know, reality is brown and gray, filthy, and poorly lit. Or at least that's what "realistic" movies claim.
Add the last-minute decision to go 3-D (which halves the apparent brightness of the movie because each eye only sees half the light), and you have a recipe for a dark, drab, visually dull film that no amount of martial arts can save.
Not to mention, let's face it, punching and having a fireball erupt from your fist looks awesome in animation, but in live action it comes across as... kind of silly.
5) There was no need for a movie: More accurately, we already had a movie, and it was awesome. "Sozin's Comet," the finale of the TV series, was 90 minutes long (not counting commercials and opening/closing credits, which bumped it up to two hours), upped the animation quality to film caliber, took the already good music up to eleven with live strings, and told an epic, world-shattering, continent-spanning tale with multiple intersecting storylines that ultimately culminated in two simultaneous final showdowns happening hundreds of miles apart.
I'd rather have a remastered theatric release of "Sozin's Comet" than a generic live-action blockbuster any day. And don't tell me you'd need to introduce audiences to the characters -- it'd be cheap enough to make (considering that it's already made)that nobody but fans could show up, and it'd still make a huge profit.
I made the decision months ago to boycott "The Last Airbender" for its racist casting choices. But I've never regretted that decision, because I always strongly suspected the movie was going to suck, and now the reviews are confirming that suspicion. Avoid this movie like the plague! If you feel the need for some epic, movie-quality Avatar action, pop in "Sozin's Comet" instead. You'll be glad you did.