YMMV / Seveneves

• Arc Fatigue: After you've invested 700 pages into the people around the Earth... almost everyone dies, time skips and you are told a fairly unrelated story about the far-future of that universe that doesn't really end neatly. The finale is less climactic, and more a slice-of-life summary of the state of the world.
• Idiot Ball:
  • It's true that Markus is under a lot of stress at the time. However Julia turning up, against all international agreements that heads of state would not be evacuated, especially when he has already been concerned that some countries may have planted sleeper agents among the arkies with a view to attempting a coup, is such an obvious red flag that letting her out into the main population rather than arresting her (if nothing else the Indian, Russian and Chinese representatives should have been very angry about the breach of agreement and demanding her head) is just stupid. The decision to allow Aida and Julia to breed as part of the Seveneves is also arguably an example, especially given Aida's explicit threats. That one is more understandable though given there were only 7 humans left (at least so far as they knew) capable of bearing children.
  • In the former case, there was probably no good answer. Explaining to the not-insubstantial number of Americans why they'd just thrown the (ex-)President of the United States, who a few days prior had fired off nukes in defense of the Cloud Ark, out an airlock (likely after basically a drumhead court martial) would likely have been tricky and arguably would have dumped bad blood in the water, leading to charges of tyranny PSAPS be damned. Doing so right before running off to the Ymir mission (which Markus knew he was about to have to do) would have made it worse since he wouldn't be around to deal with any criticism. Admitting Julia to G Pop would have caught hell from the non-American G Pop contingent even if it might have worked to keep her onside (or at least under observation).
• Nightmare Fuel: Just the idea that the human race — 7 billion people — has less than two years to live, and very little, if anything, the general population can do about it short of taking government-issued suicide pills. Mention is made of schools having to hire counselors to help children cope with their impending demise. Whatever isn't heartbreaking about the prospect of global annihilation is this trope.
• Tear Jerker: As might be expected, the Hard Rain. The goodbyes between Ivy and Cal, and Dinah and Rufus, are appropriately heartbreaking. As is the description of churches throughout the world holding apocalyptic services, with orchestras playing until the end.