I'm not sure where to start with this one. I think the first thing I noticed about it as I was reading it was that it is very, very plot-driven. I found the characters memorable more in their general description than in their particulars, which is to say: it was a book very much affected by poverty. Even the major characters who were from wealthier countries were not from wealthy or even middle-class circumstances. Everybody's life up to the point of this book was fairly miserable, and I can't say their circumstances improved much in the course of the book.
Except for one thing: they tried stuff. This was not a book about people who were beaten-down and going to stay that way. They built stuff that might be useful. They went places that might be better. And some of that didn't work, and some of it kept coming back to bite them, but they kept trying. When one thing didn't work for all they hoped for, they tried something else.
So I don't know that I could call this a depressing book. It's...rather greyish and frayed around the edges. It's not a cheerful book, and I wouldn't recommend it to people feeling fragile. But it's one that keeps trying to move forward, and sometimes even gets somewhere with it. Sometimes. Not always. Not even mostly.
A warning based on the title: while there are a few Chinese characters, this is not substantially Chinese science fiction. If you were looking for a Chinese future, this is not it.
I was pleased that Day used word choice instead of attempted phoneticized accents to indicate non-native speakers, but I was a little frustrated that years upon years of speaking nothing but English didn't ever seem to improve anyone's English. One of the characters ended up sounding like every stereotyped Asian woman in fiction to me, which was not a big plus. There was another major Asian female character who didn't sound that way, so it was clearly not an "all women of Asian ancestry sound like this" thing, but it still bugged me every time the one character came onstage with the voice of Rosie from Rosie's Bar in M*A*S*H.
Do I sound lukewarm on this book? I kind of am. I wanted to like it more than I did. I respect some of the things Day was doing with it. It's worthwhile and difficult to show people consistently trying to make the best of a bad situation. But I think the characterization is where it really fell down for me, and that didn't turn out to be optional this time around.