I have been reading the English translations and the characters and especially their dialogues feel very fake. I do appreciate the hard science aspect of the books but the long monologues, kids speaking like middle-aged philosophers, and army personnel being one-dimensional macho men breaks the immersion for me. It has the depth of a 1980s low-budget thriller.
I don’t read a lot of hard science fiction or translations of Chinese books. I don’t know if this is genre-related.
Tangential to TTBP I’d say “children of time”. Something about the writing style put me a bit off, but the story is great. It’s very plot oriented, with a saga that spans centuries without feeling drawn out. The characters, while being a bit simple, are compelling and believable. It relates to TTBP because it also talks about two competing civilizations/planets.
Without restrictions, the hardest sci-fi that I utterly enjoyed was Anathem. It plays with physics, in particular quantum mechanics, with such mastery it’s hard not to believe the conclusions he draws. And in the meantime he plays with a lot of other concepts as well. As many of the books of the same author, it tends to put too many concepts together, but it’s worth the ride.
How did I forget Dune?? I thought about how to answer your question for a day, then forgot half the answer.
Dune is absolutely great! The science is spot on, the writing sucks you in, the characters are so appealing, each with their motivation and ideologies. Everything is just amazing. It builds a whole galaxy by looking at only a handful if characters, all on the same small planet. It’s still revolutionary, in particular its focus on ecological terrorism is extremely modern.