I first read this book several years ago, and loved it. I loved the characters, the story line, the slow build-up, and the ending. I enjoy this book on a lot of levels: the characters, the real-world issues such as women's rights, specifically focusing on abortion rights, but without taking a side. I enjoy the ties to the Dark Tower series and King's universe, as well as the mythical tidbits (the weird sisters Clothos, Lachesis, and Atropos, but in a new incarnation) thrown in with the supernatural aural world.
The characters really feel like real people to me. King is good at this, but in this one, he was writing something that he wasn't actually familiar with - old age.
I love Ralph's courage and his sometimes snarky comments when faced with danger. I also respect his ability to just accept the majority of what life hands him and move on, unless he feels that he is being taken advantage of. He's stubborn as a mule then, no matter the cost.
Overall, I really enjoy this book. But, I do have to say that one thing rather annoyed me on this second reading. I mentioned before that Ralph just kind of rolls with the punches and takes the majority of life as it comes, but during the course of the story, he and Lois ask a LOT of questions. This in and of itself isn't a problem. If they didn't ask, the reader would be, but my issue is with the way they ask. Too many of their questions are rhetorical, or statements phrased as questions. IE: "We're in the library, aren't we?" or "It's 4 o'clock, isn't it?" Really? Just say, "We're in the library." or "It's 4 o'clock."
This happens so much during the book that I ALMOST knocked a star off of my previous rating. I decided to let it ride though, because I really enjoy the rest of the story. Plus, I suppose it does help tell the story, but it could definitely be improved.
Finally, I read another review in which the reviewer felt jipped by the fact that Insomnia's central plot tied in with the ending of the Dark Tower series. Everyone's entitled to their opinion, but this book was written over a decade before the ending of the Dark Tower series. All of King's works play off of each other in some way. I happen to enjoy that aspect, some don't. I would recommend giving it a shot before writing this book off.