I admit my first reaction to the trailer was somewhat underwhelming. It looked gorgeous and fascinating then the aliens showed up. And like many I thought, wait a minute when did this turn into a video game. They looked rubbery, even more so than such past CGI creatures like Jar Jar Binks. But afterwards reports surfaced from the Imax screenings that the film looks great and that Cameron does deliver.
The CGI might not be the only problem though. Several posters have suggested that the film resembles everything from Ben Bova's novel The Winds of Altair to the animated box office bomb Delgo. I am currently reading Mr. Bova's novel and while it does seem to have some similarities to Cameron's plot of Earthlings invading a peaceful planet for terraforming reasons, so does many other science fiction novels. In fact Cameron has been very forthright and admitting that Avatar was inspired by several novels he had read in his youth, including the John Carter of Mars series.
I think the problem besides the trailer is that it has been so long since Cameron has made a film that some people think he has lost his touch, that like Lucas he lost what made him a great director. On the other hand I also suspect some just want it to fail because of some sort of simmering resentment towards the fact that Titanic is still the highest grossing film of all time and we love nothing more than watching the mighty fall.
My own thought is I'm willing to give Cameron a chance. He has made four of the greatest science fiction films of the last 40 years (The Terminator, Aliens, The Abyss and T2). He knows how to work with actors (some probably forget that Sigourney Weaver actually received an Oscar nomination for Aliens) and balance effects. He's also been through this scrutiny before with T2 and Titanic where it looked like it would end his career and then he got the last laugh. With that I'm hopeful that he will deliver. And honestly, even if he doesn't you will be there December 19 to see it.