I really enjoyed this, though of course not without some minor nit-picks...
Since it was an audiobook I was really able to fly through it, I was hooked pretty immediately and honestly, I found the "extraneous" plot points, (basically anything outside of Oswald and Kennedy,) to be the most interesting and engaging elements of the story. The premise of the Kennedy Assassination brought me in, but the story of Jake Epping / George Amberson was quite beautiful and rich. 
Of course, it falls into the classic time-travel story morality shtick of "changing the past is bad" regardless of how good intentions may be, but although I knew where the story would end overall, I never found myself being bored with the journey. 
This was my first King novel and I am glad to have read it. Horror is not my genre, and the graphic depictions of violence did at times make me extremely queasy and unnerved, so I am uncertain if I will read much more of his catalogue, though I do feel the urge to do so. I will have to put my big girl pants on and be brave.