The trailer was rushed to get Cameron's approval before leaving to New Zealand for the first round of location Avatar filming. The fx are rough and in some instances total place holders. Personally I didnt care for the trailer, the Sara reveal was just here she is. But as much as the trailer gives away, its not touched much. From what I know, some FA steel balls scenes were filmed that changes things, not just what speculation and spoilers have been posted online. Seems people dont know, accept or realise Cameron has little to do with this movie outside of some ideas and concerns here and there on top of being a producer. The entire project is under another writer and director. Cameron is on Avatar indefinitely at this point.