•  "All this useless knowledge", and "Some questions will ruin you if you're denied the answer long enough". The 'doesn't need or want to know everything' Vs the scienfitic nature of exploring and being human. The tempation of the unknown. The waste of life and accumalated knowledge from the explorers. There is beauty in the uncertain, things we cannot understand and will never be able to.
•  I loved the writing dedicated to the beauty of nature, the beauty of solitude, and the peace found within exploration and losing yourself. Even the explorers not having a name didn't seem dehumanising in Area X, but liberating. 
• I loved the unsettling nature of organic beings, e.g. the Biologist's
  luminesence
  , the
  doppelgangers
  , the moaner, the
  crawler
  the dying
  psychologist
  the writing on the wall
  "Where lies the strangling fruit that came from the hand of the sinner I shall bring forth the seeds of the dead to share with the worms that gather in the darkness and surround the world with the power of their lives while from the dimlit halls of other places forms that never were and never could be..."
• There were clear themes of climate change, observation vs interference, and creeping physical and mental boundaries.  Mirroring, assimilation, remaking, copying. I liked learning about the Biologist's childhood swimming pool and her rockpool work. 
• I found the use of
  hypnotic suggestion
  intriguing.

"The book is completely fascinating and unlike anything I've ever read. The tone is eerie and unsettling in a way that sneaks up on you; because the protagonist is so matter-of-fact, there's a delay before the disturbing nature of what she's relating registers with the reader. Full of mystery, much of it unresolved, although I imagine that's what subsequent books in the series are for. I don't even know how to describe this book in a meaningful way; it reminds me of how it feels to meet literature for the first time from a culture I don't know. Parts feel familiar or "normal," and then other parts are jarringly, shockingly unknown in the way they reveal a different perspective that I didn't know existed. Worth reading again, and I think I might almost like it better in hardcopy rather than audiobook. The narrator did a great job with the matter-of-fact tone, but I wanted to go back and reread parts and see it visually on the page to get the full impact."