I thought 11/22/63 was an entertaining novel -- I had never previously read anything by Stephen King -- but you should approach it as a mainstream fiction novel, not as (1) a time travel novel, (2) a Kennedy novel, or (3) an alternate history novel. It will disappoint you if that's what you want.
That being said: it's very well-written. I get why King is as successful as he is; he really does have good command of the craft of writing. As I was reading 11/22/63, I thought, "You know, this reads a lot like Jack Finney," and then in the epilogue, King credits Jack Finney as inspiration.
So the bottom line is: if you like Finney (particularly Time and Again), you'll absolutely love 11/22/63. If you have a wide literary taste, enjoy quality writing and want a light and entertaining read, go ahead and set aside your AH critical glasses and give it a read; I think you'll enjoy it. But if you're looking specifically for alternate history (or time travel), then keep looking.