The CGI/CGA looks a lot like some of the video games my adult son plays (e.g., one called "Crysis" (sic) - or something to that effect).
It must be close to 30 years ago that a movie with Albert Finney and Susan Dey was made, called "Looker" (i hope that i'm remembering the correct movie), based upon a Michael Creighton book or screen play (not sure which; i think Creighton also directed it, IIRC). Anyways, one small aspect of the movie was a device which also had application for eliminating the need for human actors in movies - though it was used for other purposes in the movie.
Anyways, it's quite impressive what can be done with CGI/CGA, especially when humans are filmed first going through the motions. However, one aspect that appears to still be lacking (maybe i have just missed it???) is the degree of pathos or emotion that can be seen in actual human faces. Now, maybe movies such as "Avatar" don't require such considering both the plot and the intended audience. At this point, this lack of minute detail may limit the application.
Finally, I think that there is at least one reason (probably more, but for the purposes of this post one will suffice) why live plays are still popular. Plays are closer to reality, as far as the story is concerned, than Movies/TV. You are there with the actors living, so to speak, the story - immersed, both in time and space, there with the actors and viewing the story as it unfolds in real-time. Movies and TV are at least one step removed, at least in space, from this aspect present in stage plays (hence, techniques such as surround sound, 3D, etc. in movies). CGI/CGA is yet [much] further removed - especially when alien worlds and creatures are involved. Sure, cameras can zoom in on actors in TV and movies, whereas we view actors from a greater distance when they are on a stage (probably wouldn't see that drop of sweat on forming and dripping down on Dr. Edgemare's face in that scene from "Total Recall" if it were a stage play), but overall, the "reality" effect is lessened when a screen is substituted for a stage, IMO.
As we remove ourselves further from "reality", we, naturally enough, find fewer and fewer points of similarity of experience, and so find it more difficult to relate to the story.
Anyways, 'nuff said. That's my two shekels on a pretty impressive movie trailer. Hope y'all enjoy it and that it is a successful endeavor for Cameron.