The Three Body Problem
In a word
Flawless.
Recommended
Absolutely. Read it. Now.
Thoughts (spoiler free!)
This novel is outstanding, and there's really nothing else to say.
I would particularly like to commend the author for respecting the reader's time: every concept is interesting, contemplative, brief, and in the service of the plot. Where every other sci fi author goes off on self-indulgent tangents, Liu Cixin shows masterful discipline and self restraint; this novel couldn't lose a single paragraph without also losing essential context, and that's an incredible feat.
The translator also deserves special commendation.