I went into this book vaguely remembering that it was meant to be super gripping and immersive and tense and whatnot - which turned out to be true, in the end! - but was absolutely not true in the beginning. I had a hard time getting into it at first, and after turning it around in my head for a while I think I know the reason: failure to establish a clear baseline.
We're told from the start that Gyre loves caving and is very excited to get underground. We're also told that caving on Cassandra V is super dangerous - significantly more so than on Earth - and that a significant percentage of cavers die during the two or three trips they need to make to earn enough money to get offworld. Immediately afterwards, we're told that's why Gyre jumped at the chance to do it in only one. Triple the pay, presumably triple the danger, but only once. This feels like a discrepancy, and her motivations aren't totally clear - her primary reason for wanting to get offworld (which is thematically important, even!) doesn't come out until several days in, in dialogue.
So Gyre is on her first serious excursion and has no more experience than the reader, and we know already that caving has a high fatality rate even on normal excursions, and that presumably there's a reason why this one pays so much more. We also know that she (allegedly?) likes being underground, and should at least at the beginning feel pretty comfortable in her environment. Given all of that, her reactions to practically everything at the beginning feel completely overblown. She sees red flags everywhere (and yeah, there definitely are a few), she's utterly shocked when she finds out how many people have died down here before, and so on. Maybe it really is shocking! But with no hard numbers before, just a general "many people die before they earn enough to get offworld" - plus the extra financial bonus here - it absolutely didn't feel shocking to me as a reader. Gyre's overreactions are so all over the place that I couldn't get a solid grip on her character, her environment, anything. Her moral disgust at certain things also felt foreign to me - I guess she thinks it's worse when individuals do things than when corporations do those same things??? I guess a profit motivation is more palatable to her than a personal one???? Because capitalism?????
Gyre is the viewpoint character, and Em - who exists mainly as a voice in her helmet, and is the only other major character - is presented from the start as manipulative, untrustworthy, and dangerous. Which makes it awkward that I found her significantly more relatable than Gyre, at the start. "Relatable" isn't even the right word - "predictable" comes closer, but really it's something between those. "Reasonable", maybe. I didn't know her deeper motivations, but I could understand why she did the things she did, follow her logic, &c., in a way I couldn't with Gyre. Even when she lied, I felt she could be relied on to have Gyre's safety at heart: completely counter to the way Gyre thought of her.
This all sounds very much as though I didn't care for the book at all, which to be honest was kind of true for the beginning - which makes this book one of the biggest differences between how I felt about it at the beginning and the end that I've read yet.
I can pinpoint the exact moment it turned around, though I won't because spoilers. The point is, once things started changing, the beginning up to that point became the baseline - which meant that all at once Gyre's emotions and reactions felt much more grounded. Somewhat ironically, seeing as Gyre herself began to be considerably less grounded, but there it is.
As of that point: it was gripping, it was immersive, it was tense, and I enjoyed it. There are basically two components to it: survival and trauma bonding. There are high emotions all over the place, often - but not always - because of immediate physical danger. There's a lot of immediate physical danger! There are lot of very thin margins! There are a lot of things going wrong when the margins are already very slim! Which is all to say that it may be a cathartic read for some people, but it is certainly not a relaxing one.
Selling points: it's a survival story with trauma bonding and a [somewhat spooky?] cave in a sci-fi wrapper, plus also lesbian rep. Either you like that sort of thing or you don't!
Warnings: unreality, loss of autonomy, few calm moments between the tension; takes a bit to get going.