Both novels begin roughly five years before the Kennedy assassination and both books more or less end on that day in Dallas. Yet, neither book is really about the JFK hit. That's just the McGuffin.
What both books are about is what American life was like after World War 2 and before Jack got whacked. Both authors are roughly the same age (King was born in 47 and Ellroy was born in 48) and both books let the authors examine America as it existed in their childhoods.
Both books are clearly very well researched and many of the same characters pop up in both books. (Dwight Holly, James Tippet, etc...) King is much more interested in Oswald's life than Ellroy was, but since the killing isn't the real subject matter that doesn't make a shitload of difference.
What does make a difference is how completely differently both authors see the years between 1958 and 1963. Part of this, I expect is because Ellroy is very right wing and King is very left wing. Part of it may also be that Ellroy grew up in a city and King did not.
Most importantly, however, I suspect King liked his childhood (which is why he revisits those years in so many books) while I know that Ellroy's childhood sucked (his mother was essentially an amateur hooker who was killed by a serial killer and then he was raised by his alcoholic neo-Nazi dad.)
So, Ellroy paints those years as gritty and violent and sees a world of greed run by rich white men behind the scenes who game the system at everyone eles's expense.
In fact in the preface to American Tabloid, Ellroy writes: "America was never innocent. We popped our cherry on the boat over and looked back with no regrets. You can't ascribe our fall from grace to any single event or set of circumstance. You cant' lose what you lacked at conception."
King, on the other hand, is very nostalgic and while he acknowledges the flaws in the system seems to think that 99 percent of the people in the late 50s/early 60s wanted to do the right thing, that most people were honest and that life was generally better than it is now. Things taste better. People communicate with each other more. People are more charitable then they are now.
What this means is that Ellroy's theme in American Tabloid is that the JFK hit didn't change things much. That corrupt white men ran the system before the hit and corrupt white men still run the system today.
King, on the other hand uses his book to ask the question - "Would things be less shitty today if JFK had lived?" That question could only be asked by someone who thinks things were better back then.
That makes for an interesting story because it allows King to create sympathetic characters who we want to cheer on. Most of the story takes place in a Texas town called Jodie and by the time November 63 happens we feel like we not only know the town, but would like to live there.
King can be a master at world building when he wants to be and he world builds excellently here. And, for once, he's created a long book that doesn't have a disappointing ending.
My one and only problem with the book is that I don't buy King's premise at all. I do think things were not that much better back then then they are now. In many ways, we've made strides forward.I do think that corrupt assholes still take advantage of the system, but I doubt it was that much different back then. I hate King's rose tinted glasses about that era.
But, at the end of the day this is a yarn and it's a damn good yarn, if a bit too left-wing nostalgic for my taste.
Bottom line: I liked the book even though I think it's full of baby boomer propaganda bullshit, because I liked the characters and it was interesting to see the same events in American Tabloid shown through a different set of eyes. But, at the end of the day if you want to read a great story about the JFK hit, Tabloid is far better. If you want to read a happy nostalgic Stephen King story, on the other hand, and don't give much of a shit about the JFK aspect then 11/22/63 is a winner.