Who let M. Night Shyamalan direct Avatar: The Last Airbender? You can find fault with the script, the acting, the conceptual direction of the movie in relation to the fantastic television series, but my complaint is actually technical. Shyamalan is exactly the wrong guy to direct a 3D movie.
For the 3D effect to work, a director needs to have a parralax effect, that is the position of objects in space needs to be different as percieved by each of the two eyes. To get good depth perception and parallax, you need a great depth of focus.
Other commenters have criticised James Cameron for using a limited depth of focus where the background is blurred as a trick to accentuate the 3D effect. ( I must confess that I haven't seen the movie yet). In Cameron's case this technique is deliberate because most of the scene backgrounds are CGI. I think it is a poor choice because such focal effects are contradiction to how we perceive the world with our adjustable focus stereoptic vision. In real life we look in the background to check out the visual information there, then refocus on the foreground. When directors take this ability away from us, it diminshes the immersive effect dramatically.
In the case of Shyamalan, there is no choice. This director is a one trick pony, almost every scene in his dark movies has some depth of field effect blurring either the foreground or the background. In addition, he compresses the dynamic range in the shadow detail. When the two techniques are combined, background winds up not only blurrily out of focus but also dark. This doesn't help the 3D effect which relies on the clear differences between the image delivered the right and left eye.
The source material for The Last Airbender is 4 seasons of an animated television cartoon. Although many scenes of the television show take place at night and tend to a darker palette of colors, edges are sharp, outlines are defined and the art direction is colorful (cartoon-like, go figure). Why the production of the movie would depart from this so drastically and for what effect, I cannot imagine. I am not sure that M. Night Shyamalan is capable of making a good movie of Avatar, the Last Airbender.