Quite a fascinating topic: if you could travel back in time and change one significant historical event, would you do it? What would be the repercussions of the change? In this novel, the event is the assassination of John F. Kennedy. The story is very engaging and involves the changing of other, less historically significant events as well. A side topic: what would you do for the person/people you love?
The novel is written in a completely believable way and a tremendous amount of research was done in order to keep as much of the historical data accurate, including information about Lee Harvey Oswald and the people with whom he associated. Although, King does take some liberties that he freely admits to at the end of the book.
11/22/63 is a great read (this from a person who typically does not enjoy history even in a fictional setting) and I highly recommend it.