One of my favorite books so far this year is Mr. Mercedes by mystery/horror author extraordinaire Stephen King. There are many great reviews of this book on www.goodreads.com. I'm not sure what I can add that's not already out there. I thought it was a brilliant, page turning thriller and recommend it highly, even if you're not a Stephen King fan.
I hope they make a movie out of this book someday! I hear there will be a sequel released next year called Finders Keepers.