I often wonder if it's the writing that's bad or the translation.
I really get the impression lots of the sentences and paragraphs are stilted translations which don't succeed, either because of the translator of the inability of english to express the nuance of what the artist meant. To be clear, I think the latter limitation goes both ways, indeed any time you are translating between languages.
Ken Liu, who translated the first and third books, is a respected English sci fi writer in his own right, as well as being a native Chinese speaker.
I felt the same as you about the prose but, given Liu’s background and having read his other books, I assumed it was an intentional choice. Based on his other work, Ken is a good enough writer to know what he was doing, and the sentence structure was probably a balance between translating the ideas and translating the form. You can definitely argue with how it worked out but I do think it was mostly intentional and not a lack of writing or translating skills on the part of Ken Liu.
I will say, the middle book, “The Dark Forest,” was translated by someone else, and it felt way different to me. Sentence structure, pacing, themes, stuff that would be way out of scope of a direct translation. I always wondered how much of that was the original and how much was the translator doing more adaptation to make the whole book feel like a native English novel.
i read the three-body problem in chinese, but didn't read the translation. my impression was that liu cixin's writing isn't very literary - he rarely uses rhetorical flourishes or idiomatic expressions, and his vocabulary is very simple outside of technical language. however, it's very straightforward and accessible.
someone else i know described the novel as 'clearly written by an engineer rather than a humanities student,' and i think i'd agree with that description.
Engineers and scientists can be like that. Perhaps the most obvious English-language one is Andy Weir (The Martian, etc) where the characters can feel like they're agents implementing an story rather than part of it. But certainly author-first authors can lean into this too and end up writing basically a narrative report rather then a story.
Which is, to be clear, completely fine: sometimes the characters aren't actually the core of a story, especially when dealing with substantially non-human-scale subjects and abstract concepts. It's also much more of a challenge to keep characters front and centre when on a very large sci-fi stage. It's easy to concentrate on the people when it's just a few people in, say, a regular house, just doing human things. I think some of the genius of Iain M. Banks especially is that he manages to somehow place the people (and non-people like Ships) dead centre even though the stories are ostensibly on an incomprehensibly vast scale. It's one of the few sci-fi universes where I think first of the characters and not of the universe in which they exist.
The original Star Wars and Dune also had particularly good character-centrism, where the universes were clearly enormous and could be arbitrarily detailed, but existed to support the characters journeys rather then the reverse.
I ran into that issue when trying to read Yoshiki Tanaka's Legend of the Galactic Heroes. The translation for the first two books in the series was ok but not amazing, but for the third book they changed the translator and it became a complete and utter mess. I remember one part where a character says the complete opposite of what they said the previous sentence, and I'm 99% sure it was an issue with the translation and not with the original Japanese.
Still better than the copy of Miyamoto Musashi's The Book of Five Rings that I once found that appeared to have been copy-pasted into Google Translate at least.
I really get the impression lots of the sentences and paragraphs are stilted translations which don't succeed, either because of the translator of the inability of english to express the nuance of what the artist meant. To be clear, I think the latter limitation goes both ways, indeed any time you are translating between languages.