These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Harsher in Hindsight: While telling Jake about the horrific history of alternate!2011, Harry mentions that "four of the Japanese islands are gone" due to the Earth's increasing seismic instability. This may or may not count as a "Funny Aneurysm" Moment, since most of the book was completed by the time of the 2011 Tohoku earthquake, but the actual quake is later mentioned in the story. Speaking of the Japanese disaster, also worth mentioning is how in the alternate timeline a nuclear meltdown in Vermont irradiates much of New England.
Hilarious in Hindsight: In The Langoliers, it's mentioned that because of the way the time rip works in it, you can't, say, go back and stop the Kennedy assassination. And then this book gets made...
Jerkass Woobie: Oswald is depicted as a somewhat sympathetic character.
Narm: Jake punching Sadie's ex with a cry of "This is forthe broom!" While it's true that denying your partner sex is considered a form of emotional abuse in some cases, this is after the guy has kidnapped Sadie with intention of killing both her and Jake himself, making the righteous outrage over that particular thing seem... misplaced.
Harry Dunning. Not only does his essay move Jake to tears (and help inspire his journey), the universe shafts him in all three timelines; in the normal one his dad murders his entire family and cripples him (Harry) for life, in the next one he's killed in Vietnam, and in the final one he's left paraplegic in the war.
Sadie Dunhill as well. She was married to an abusive lunatic who later returned to cut her face severely, and almost killed her, and its implied her mother enforced this relationship just to look good in front the lunatic's family. Her current boyfriend, while nice, spouts unusual nonsense and she dies trying to stop Lee Harvey Oswald. Luckily her life in the normal timeline is full of civic achievement.