I'm going to give this a 3.5 and round up. There's a lot to appreciate in this book. The author's description of our protagonist's (Iris Cohen) life is the perfect buildup to her decision to emigrate to Nyx. She leads an apparently privileged (she has a job that pays enough for her to live decently and party) but absolutely hellish (meaningless work, meaningless relationships, drinks hard and eats horribly because all her friends do and then feels awful later) life. She hates what she does and it seems like an endless treadmill. Her family relationships are not enough to keep her there. Though she would have liked them to be. So off she goes.
The world of Nyx seems artificially constrained in a way that makes it feel like it's fake. Sauma spends no time explaining the science at all, just says one gets there through a wormhole and briefly describes what it looks like. It's all about what Iris goes through. The participants are weirdly cut off--they can (and are required to) post about their lives on social media, but they are not allowed contact with Earth and so never get feedback on what they are doing.
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The writing is excellent and I feel like I understand Iris. It's not a book to lift your spirits but it's worthwhile.