So I've just finished this book. First the obvious caveat, it's SK, best writer ever, I feel privileged to live in a time and place where I can experience SK in my life and I would read his shopping list.
Didn't particularly enjoy the book. The writing was an engaging as ever but the ending.... I think this was just something he had to get off his chest. He writes in skeleton crew that every horror writer has to, at some point, tackle the abyss, the horrible void, the terrifying wasteland that lies belong this world, Lovecraftian style, and he's done a few short stories about it. Including a few with the worm book in them. This was his attempt at turning that into a novel I think. Didn't really succeed and I think this was because he started with the premise that he was going to write a novel about the abyss, and then shoved some characters in to fit. I would wager that his novels are usually more organic than that.
Plus the "secret electricity" thing. When you think of the complexity of the universe he showed us in the dark tower series and how explicitly he explained that, the secret electricity was a total cop out. It was just "yeah, here's a plot device, don't ask questions, just accept it" and he doesn't t do that normally. He explains. It's why you believe his world building. This was thin.
Also, I didn't enjoy the fact I couldn't relate the book to the DT universe. I want that to be the core of his books and I always enjoy them more when they are. Not that they have to explicitly reference DT in any way, just that when he writes within that framework, they are the most compelling and wonderful books he writes. Personal thing though.