I consider Neal Stephenson to be one of the modern Grandmasters of science fiction, right up there with David Brin, Greg Bear, or William Gibson. I have not, however, obsessively read everything he's written, as I did with earlier Grandmasters (Asimov, Heinlein, Clarke). For one thing, I'm a grownup now and don't have the time I once did. Also I have branched out quite a bit in my reading, and have come to concede that even Grandmasters do not create all their works equally. I could not manage to get into The Baroque Cycle and put it down after Volume 1. But I got Seveneves as a gift and looked forward to reading it.
And am really glad I did. This is throwback SF in the best possible way--informed socially by the present, and packed with fascinating descriptions of ideas for what's coming in the future.
We start out with a bang as something that comes to be known as the Agent rams through the Moon and breaks it up into seven big pieces. Pretty shocking stuff, but it looks like life will go on, until scientists start crunching the numbers and figure out that life won't, in fact, go on. The Moon will continue to break up into smaller pieces, and those pieces will come down on the Earth in a five thousand year firestorm.
Stephenson plays out the story in Grandmasterly fashion from there, telling a compelling story of humanity's efforts to allow at least a few to survive. The focus is on setting up a space colony. That colony barely squeaks by, but get by it does, and eventually builds a thriving society that prepares to resettle earth.
There are several well-done characters in this book, but in truth it stands out as a work of ideas. We have the survivors deciding to divide the human race into seven different races, for the most part cooperating but with some deep divides. Lots of orbital mechanics and physics along the way. The story is a great one for geeks and keeps you wanting more all the way through.
Stephenson is good with different literary voices. Cryptonomicon (a follow-on to the Baroque Cycle, but written first--a post-quel?) is very geeky but businesslike, and The Baroque Cycle somewhat flowery, as one would expect. Snow Crash (his breakout) is very Cyberpunky. For Seveneves, he chose--dry. Not as dry as Jack McDevitt, but dry nonetheless. I wondered why, as he doesn't have to write that way, and have not sorted it out. Most of the characters are scientists, maybe he's trying to be true to their type? The bartender departs from this with somewhat--dry--humor.
Also, the book jacket kind of has spoilers in it. It gives away that humanity really does survive, which was in suspense for awhile.
All in all, it's a terrific book and you should go read it if you haven't. I give it 4 stars.