First part: 3/5
Second part: 5/5
Third part: 3/5

Seveneves is a nice hard SF, with emphasis on "hard" and "science" parts, not on "fiction" one.
Storytelling and character development are totally neglected (except for the second part).
People behavior is hardly plausible. E.g. would anyone believe that the entire Earth population accepts its fate peacefully in the first part, and that there are no disturbances at all besides that minor Venezuela one, two years later? Or that, in a thousand years of living together, different races wouldn't mix, and wouldn't dissolve in each other? (It is suggested that "old racism" is dead - then why there are only sporadic cases of interracial marriages?) Certain scientific ideas are hardly plausible as well.
And the author himself acknowledges that the third part is more of a tech show than a coherent sensible story.

It's hard to give this book even four stars, having read works by [a:Greg Egan|32699|Greg Egan|https://images.gr-assets.com/authors/1375595103p2/32699.jpg] and [a:Vernor Vinge|44037|Vernor Vinge|https://images.gr-assets.com/authors/1215099239p2/44037.jpg].