Some movies belong in that fridge category. You watch them and then late at night your tummy is rumbly. You get up and while standing in front of the refrigerator a thought crosses your mind about the movie and you're like "oh, man that's what they meant by that?" Then if you are like me you eat a burrito and go to bed. Annihilation will make you think twice about the burrito.
So Natalie Portman plays a military scientist lady whose soldier husband went missing a while back. Then he pops up all spitting blood, like you do, and gets taken back by the military. Portman is like "whaaa" and the army is like "uhhhh look at the shiny thing." Portman is then recruited into a team of fellow military scientist ladies and they venture into the shiny thing. Inside, they see mysteries all over the place as something is combining DNAs to form new things like sharkgators, plant people, and a flower. They do not meet Mulder and Scully, spoiler alert.
Look, if you saw the trailer, you saw a bunch of trippy shit that is the set dressing for this movie. For the most part, the story here is as basic as the last Mad Max: go here, do a thing, try and get back, and look awesome doing it. Inside this movie are a lot of stoner thoughts having to do with the nature of man, replication in nature, and the divide between what man has become after (s)he has left the food chain. It's really trippy and there's a good chance some very solid substances should be imbibed before getting into the types of stoner philosophies this movie projects. They could also help with some of the more screen-saver like special effects that while trippy are not very believable.
Go watch this one if you want to think on a movie for a few days before finally realizing it has little to say beyond what's up its own ass. It's fun and a nice solid horror fantasy story with more ideas than speculation.