I agree - I recommend Seveneves to anyone, but I say stop as soon as Act 1 ends. I think Act 2 spoils the ending of Act 1 by undermining the high stakes that made it impactful.

I can tell Stephenson enjoyed writing Act 2 as an act of fun semi-hard sci-fi, but I think it should have been in its own setting, not tacked on to a dark hard sci-fi survival novel.