As I've said before, I thoroughly enjoyed Meyer’s novel, which is told from the perspective of Wanderer, a thousand-plus year-old alien whose species invades Earth and takes over the human population. The aliens, called Souls, are inherently altruistic and abhor violence; their preferred method of invasion is a gradual and quiet take-over of individuals until the entire population of a planet is inhabited by Souls. Earth is the ninth planet for Wanderer, who has been on more worlds (and thus inhabited more species) than most Souls, who tend to settle on one of their first several planets and live out the rest of their lives there. But Wanderer soon discovers that humans are different than any other species she has inhabited—most particularly in that her host (a girl named Melanie) refuses to surrender herself to Wanderer as all her other hosts have done. As Wanderer spends time on Earth and forms a relationship with her host, she starts to rethink her species’ philosophy and intent for the planet.
In addition to the twist on alien invasion stories (by telling it from the perspective of the alien), I was particularly intrigued with the themes related to altruism and how this story invites us to examine our own understandings of what is in the best interest of others—and challenges us to be open to allowing those understandings to change as we engage with and listen to the stories of others. (You can read more about the novel and my take on it here.) It’ll be interesting to see how this theme—which is fairly major in the novel—translates onto the big screen.
We're starting to get a good idea of the differences between the novel and the film as the trailers emerge. Right now, the trailers (the second trailer more so than the one above) are revealing the story somewhat chronologically, showing us Melanie's life before Wanderer occupies her, whereas the novel is told entirely (with the exception of a coda) from Wanderer's perspective beginning with her occupying of and waking up inside Melanie as her host.
In addition, the trailers are focusing on the outward plot of the invasion and the resistance and still doesn't give us much of a hint on whether the more inward journey of Wanderer, which was on the front burner in the novel, will be explored in any great depth. We are getting some hints, however, at the internal interactions between Wanderer and Melanie in brief points during the trailers and this featurette talks about that a little.
You can view the other trailers and featurettes for The Host on the film's official website.