I loved this story when I read it, which was more than once. Because I knew the story, seeing the movie didn't phase me as much as it might of for someone that was seeing the movie without knowing the story.
However, I believe the lead actress could have worked with her character better. It was very slow, lacked the passion I believe the situation of the story needed. It needed to get across the desperation. It needed fiery character presentation. The duality of the lead character needed to be more apparent besides just a plain voice over for the second entity. The most passionate person was the seeker's character.
I would love to see this movie done with a few new cast members, but keep William Hurt for Jeb. Also, more apparent changes in the new world, little nuances that indicate that there is a new alien race. And given each 'soul' has lived different lives, show little traces of those lives in the architecture and behaviors. Souls that had lived as a plant, would on earth surround themselves with plant life, live very natural perhaps. Souls that had been beasts, have the company of wild cats or bears, things like that.