My vote is for Super Blue (or, What Keeps On Floating), by @deeanndmathews!
I was totally engrossed by the naturalness and veracity of the prose. It really seems to hear a speech given by the protagonist, an "astrotrasher" who, with his lexical mannerisms and his colloquial register, has unfolded a future but fully plausible world with a very strong internal coherence.
Not just a beautiful science fiction story with solid scientific foundations and a very strong ecological perspective.
Also a masterful example of how one can intelligently and compellingly contravene the "show, don't tell" principle, avoiding the point of view of an all-knowing narrator who only wanted to explain in a didactic manner.
The message is finally very strong and it touches us all very close.