If you read the book first, how did you feel about the film?
I had just finished reading the first novel (and so far, just that one) a few weeks before seeing the film. I was surprised at the number of changes made, not just omissions, but entirely new ideas and scenes were created for the film. It gave me a sense of disorientation while watching, which isn't always a bad thing (especially for a sci-fi thriller like this one), but there was also a part of me that was questioning whether these changes were made for valid reasons integral to the story the film was trying to tell, or done just because they were supposed to provided some thrills to keep ADD-afflicted audiences entertained. Such as the Mutated Bear scene (nowhere in the book), or the final machine-gun blasting of Portman's doppelganger alien for the big climax (also made-up for the film). These two specific sequences left me wondering if they were just discarded pages from an unused script for the Alien series.
The story in the novel is told in a first person narration by Portman's character that serves to explain a lot about her motivations so as to engender some sympathy for her since, on the surface, she doesn't come off as being very sympathetic at all. She's not even really in "love" with her husband, at least not in the sappy tickle-in-bed sense that they are in the film. But she is loyal to him, which is why she goes on the mission. And not to find a cure for him, either, because he's dead by the time she starts the mission.
The tone of the book also presents the foray into the affected area more scientifically than the Jurassic-Park type adventure it's portrayed in the movie. From having read the book, I was expecting a more cerebral, Terrence Malick-type of film that would have retained the narration by the lead character. Also, the book leaves the origin and intention of the contamination ambiguous and unexplained, which the movie discarded with it's extraterrestrial slant. But of course we all know how well modern audiences hate ambiguity, so that wasn't a surprise (need to justify your budget somehow).
The movie was definitely a different animal than the book was (in more ways than one, I guess). I'm surprised the author of the novel went along with these changes since he worked on the script with the director.