The Waves is a type of SF story I particularly like--the eternity/galaxy spanner. There are many like this, but my introduction was Mike Resnick's Birthright: The Book of Man. It's tough to pull off in some ways, because there are so few constraints--pretty much anything might happen. And none of it is particularly likely, because I don't think we have the capacity to imagine what such post-human life would be like. But it's great to make the attempt.
Liu's story explores how star exploration would proceed, given that technology would continue to advance back home and the generation ships might get passed. I recall reading a classic SF story with this theme, but the name is not coming back to me--another time, perhaps. In any case, Liu handles the tensions and choices very deftly, through telling stories within stories. It's a very satisfying story to read, and I can heartily recommend it. 4 stars from me.