By now any discussion of the adequacy of the Avatar posters as a marketing instrument have been rendered useless. The film is big. It will make lots of money. Whether the posters helped that a little or made the path to the top a little harder is of little importance.
A more interesting question right now is how the posters works as iconic images for the film. After all the film has been seen by many, many people, several of whom must have loved it. And the posters seem to be selling well. But will those posters work as a reminder of the things that people liked about the movie? Will they take them back to that experience? And will their images serve as an icon that we will often remember when thinking about the film?
My own guess is probably not. Avatar is an specifically difficult experience to capture in a 2D still image, for obvious reasons. In order to overcome that you would need something very creative and inspired, and the posters strike me a rather bland and generic.
The posters that show both Jake’s and Neytiri’s floating heads, with some Pandora images in the middle remind me of the poster for Titanic. Show us the two leads who are romantically involved and the backdrop to their relation which makes this a very special story (Pandora in this case, the boat in the former). But the Titanic poster was a much more significant achievement design wise, managing to not just show the characters faces, but also their relationship, and mixing that in a much smoother way with the backdrop, resulting in an evocative and beautiful poster. And yes, it’s much easier to show the Titanic in an image than to show Pandora.
The poster showing just half of Neytiri’s head does better in this aspect by very much giving up on being in any way representative of the film as a whole. It shows just on aspect of the film (the blue people!) and one character, and even then only a little bit of it. The image is sufficient to trigger the memory, but doesn’t go farther then that, allowing us to fill what is behind the image with our own imagination. Not brilliant, but reasonably effective.