I nearly DNF'd (Did Not Finish) this book after the first chapter. I was bored by Augustine's story and the writing wasn't at all compelling. It felt very clinical in a way. There's a lot of exposition without much emotion/development from the character.
Also, Augustine reminded me of Ove from 'A Man Called Ove' in the way that he is this cantankerous, miserable old man that we're supposed to love in spite of his grumpiness, but I found really off-putting. In both cases, we find out that they aren't grumpy because they're old men, but that they've always been anti-social (and in Augustine's case, bordering on sociopathic.) There are passages throughout the book where I was compelled by his story, but then we would learn something about him that just made me dislike him even more than I had before.
I much preferred Sully's story, but she isn't exactly a paragon of humanity either. At least that part of the story had multiple characters, and dialogue.
The twist that they are father and daughter and that the child he finds is a) imaginary, and b) a manifestation of the daughter he never knew was something I'd worked out relatively early on. And honestly, the odds that two of the last people able to communicate with one another via radio in the entire solar system just happen to be long-lost father/daughter is a little ridiculous. It definitely stretches my ability to suspend disbelief.
Also, the fact that we never learn why all communication has ceased is a little annoying. I have to wonder if the author even has an idea as to why. If there was a war or pandemic, it wouldn't make sense for all of the people in the Arctic to be evacuated at the beginning of the book. Evacuated to what? Certain death? And why wouldn't they tell the people working in the Arctic what was going on? Saying that there won't be a return trip isn't an explanation, and it felt like the author had her characters be purposefully vague in a situation where it didn't make sense. If you are someone who needs a story to be wrapped up, skip this one. It's very open-ended and has zero resolution.
All that said, I would LOVE for this to be made into a movie. I actually think it would work far better as a cinematic experience than it did as a literary experience.
At the end of the day, I am glad I continued past the first chapter, but I don't think this book is for everyone.

One last thing, the audiobook for this didn't work for me. The voice actors had good voices, but they were very dry, especially the man narrating Augustine's part. Part of that is to do with the dry writing style, but it felt like he was reading me a text book. I listened to the audiobook while I was doing chores and then switched to the physical copy when I was done and found myself much more engaged by what was going on in the second half of the book. I think if I'd continued with the audiobook, my rating may have been lower. Just goes to show that a bad audiobook can harm a decent book as much as a phenomenal audiobook can boost a mediocre book.