After blowing through the Southern Reach trilogy to begin the year in anticipation of Annihilation, lets just say that I went into the movie with a good knowledge base of what could happen, even with director Alex Garland reportedly making his adaptation his own. In all honesty, reading all three books took me out of the film just a bit because of how much was actually changed in the transition.
From this point on there will be spoilers galore to both the film and all three books, so if you would like to avoid said spoilers, feel free to peruse the rest of the site and pick up some collectibles in the store.
To save time, I'll just say what the movie didn't change: The Psychologist (Jennifer Jason Leigh) has cancer, something that isn't revealed until book three if I'm not mistaken. That's pretty much it.
Even in watching the previews for the film you can pick apart the differences, such as there being five expedition members, those member carrying weapons, etc. In the book there were only four members of the expedition, with the Linguist getting cold feet before entering Area X. The four women set up base camp at a predetermined location, and while they do spend nights away from base camp, they aren't meandering around Area X looking for a place to set up shop each and every day. In fact, their main focuses in the first book is the lighthouse and the topographical anomaly.
While the topographical anomaly (or tower as the Biologist calls it) is not necessarily seen in the film, there are traces of its existence in the hole that Natalie Portman climbs down inside the lighthouse at the end of the movie. Not the staircase or the words that seem to be moving scrawled on the wall, but the room does pulse a little and there is a being of light at the bottom. In the book, that being turns out to be the Lighthouse Keeper, seen by The Biologist in a picture in the book version. The Lighthouse Keeper even gets his own chapters in the final book of the trilogy for added context as to what came before the creation of Area X. With the timeline of how long ago the comet hit being minimized to three years (~30 years in the books), it's understandable that Garland moved away from the Lighthouse Keeper story, but it also means that we're unlikely to see the younger version of the Psycologist playing on the rocks in by the lighthouse any subsequent films, too.
The storyline of the husband (Oscar Issac) is true at its most base form - he went into Area X and made it out, but something was wrong with the man that returned- but he dies before she goes into Area X.
One bit I found odd in the film was that the Southern Reach (the facility outside Area X) didn't seem prepared. Natalie Portman's character, Lena, shows up when they whisk her husband away, and with a new expedition planned in six days' time, she gets to join the party. That could be because of the relatively new existence of Area X, with more time needed to work out the kinks, but it seems like adding a new member on such short notice with little training is a pretty terrible idea.
One part that I liked from the books that was completely absent in the film was the use of hypnosis by the Psychologist on the other members of the party, and really only because of the confrontation between the Biologist and the Psychologist towards the end of the first book when the Psychologist is laying on the beach outside the lighthouse, injured, and she screams, "Annihilation! Annihilation!" at the Biologist, who has figured out that she is somehow immune to hypnosis. It was a much better use of the title, given the raised stakes of the scene and the fact that the command was supposed to make the Biologist kill herself - if it had worked.
My two favorite parts of the movie - the bear monster scene that was filled with tension and the "mirror" scene in the lighthouse (it may just be the sound the copy makes) - don't exist in the books. There is a Biologist clone, or copy, in the books, but that is unveiled in book two after she tells her interrogator after days of questioning that she isn't the Biologist. That could theoretically still happen because anything seems possible in this world and Lena had a shimmer-glint in her eye in the final frame of the film, but I'm not counting on it.
The second and third books are mostly predicated upon secrets. The Southern Reach names a new director (he goes by Control or John depending on his mood) after the Psychologist departs, inserted largely due to the influence of his mother, unbeknownst to him. His ultimate boss, however, is the sole survivor of the first expedition into Area X, someone that the Southern Reach has deified, Lowry. Control's mother and his new boss are seemingly filled with answers, which we actually don't really get in the books. It's more of a choose your own adventure to be honest, but if there are more Southern Reach films, Lowry certainly won't be a part of them, given that Lena's husband was the first person to "survive" an expedition.
Again, pretty much everything in the film was at least skewed, if not changed completely, but these are the changes that I found to have the most impact on distinguishing the books from the first film.
The books were entertaining, but I was always hoping for more of a reveal, a twist. The few that happened were pretty predictable. With the separate path that Annihilation took on screen, it's still possible for the story I was hoping for to become a reality, though whether another movie in the series gets made is entirely up in the air.
Annihilation will be on Netflix Monday, March 12, and I'll definitely be watching it again, if for no other reason to put the book version behind me and give this new adaptation my full attention.