One of the few science fiction movies where both the science and the plot hang together and they don't loose track of the details. It is very expensive to grow an avatar body, so only the science types have one, the grunts have only the original human 1.0 version, except for the hero who is twin to his late brother, the PhD who spent three years learning the autochthon's language. Being identical to his late twin, he gets an avatar. By the way, every penny they spent on special effects was well worth it. This is a fully realized alien world (well, moon).