I enjoyed it, even if I adhere to the conspiracy theory re JFK. It was overly long but that's to be expected from King now. At least I finished it - I've picked up several of his over recent years and not gotten past a few chapters. And the ending was particularly good, particularly the alternate history set out by the hero's actions.
This would have to be one helluva long movie. I think like a lot of King fare it might work better as a miniseries.