I think Mr. Stephenson is more effective in the thriller/adventure space than in the pure sci-fi genre. The premise of the moon breaking apart is good and tension builds nicely, but after so many 'crap-can-go-horribly-wrong-in-space' episodes I began to think - Ok, let's get on with the story.
As an example, things go horribly wrong again and again in 'Reamde' but given all the geographical locations, modes of travel and a much larger cast of characters it doesn't feel as contrived as it does in 'SevenEves'.
Then there is the ending. Or endings.
I am not going to say the ending (the last fourth or fifth of the book) does not work. However, there is no segue-way to it and feels more like an appendage than part of the main story. My opinion is the 'first' ending would have worked better and expand the second ending as a sequel or perhaps a novella. Either way the last fourth or so of 'Seveneves' stands alone and should be separate, or at least distinct from the major part of the novel.
If you're a Neal Stephenson fan you have probably already read 'Seveneves'. If you have not read any of Mr. Stephenson's work I recommend starting with 'Snowcrash' or 'Readme'.