I liked the entire book, and the ending for that matter, but I've seen some who thought it was stupid and came out of nowhere. Personally I find that rather daft considering how the book is set up, but if you aren't familiar with the author whom king took inspiration from in writing the book (probably a spoiler to say, so I won't) I could see how it seemed like an ass pull despite the warning signs everywhere in the book for fans of aforementioned author to catch.
Then again I think it's kind of odd to be reading king and not have any experience at all with that author, but I guess there are all kinds of people out there who read King's books.
Personally I think revival is one of the best modern king books. Some think it's too slow, but I loved the slow, aching burn in the lead up to the explosive ending.