In a word
The film wore it better.
Indeed, the film was excellent, and I chose this book specifically because I enjoyed the film and wanted more. I don't have much to say about the novel; it was competent, but I think it managed to ride out mostly on a wave of good-will generated by the film. Barring that good-will, it combined the subject matter of Joseph Conrad, Edgar Allen Poe, and H.P. Lovecraft, so there's nothing really new to see here, which is disappointing.
The novel also ended without providing any answers to significant questions. Ending with the protagonist saying "I will not find any answers" is a cop out, as well, which is unimpressive.
Perhaps the most significant takeaway from Annihilation is discovering my new new pet-peeve: ending sentences with "entire". For example, he was able to see the entire world, vs he was able to see the world entire. Doing so is likely grammatically incorrect ("having no part left out" vs "consisting of one piece"), but more importantly, it's pretentious, and a lazy way to add gravitas.
Nevertheless, I will probably continue with the series. I already bought the set, they're comparatively brief, and now that I'm caught up with the film's storyline, things will hopefully get more interesting. Stay tuned.