I was pretty intrigued when I started reading this because it was both my first 'modern' King, and first non-horror book of his I’ve read. Things like 'The Voice' being mentioned were weird to me as I'm used to 80/90s references of his earlier works, but this did not affect my reading experience. The audiobook narration was also really great, especially in the opening section. 
And this is where the issues lie... The first section in the 'real world' was really good. I loved the dynamics and mystery of the story unfolding, and Mr Bowditch definitely wormed his way into my heart a little. 
But as soon as Charlie stepped foot into the fantasy land it all went downhill. I read in another review that it was like two completely different books sandwiched together, and I definitely agree with that. 
The fantasy elements were SO dull and bog-standard - there were absolutely no original or stand-out ideas. The same repetitive 'journey' narrative just kept GOING and GOING, with nothing of value happening. Maybe if King had tried to write this as a shorter book, cut a lot out and stopped overindulging his ego, it would have been better, but judging from reviews I've read about the end of the book, I doubt it. 
I think I'm coming to realise that King just can't write good long books - 'Insomnia' springs to mind, which had the same vibe of an interesting and intriguing premise, then pages and pages of meaningless nothing. Even my love for Radar (who for some reason I kept imagining as a golden lab) wasn't enough to keep me interested. 
One of the most egregious things is that there's no real drama or tension - Charlie just kept being brilliant and completely capable of everything he ever tries. I’m SO sick and tired of books with no conflict or struggle!
After reading MANY reviews which say that the slow middle section isn’t worth it - that the story just peters out at the end rather than having a satisfying climax -, and that the first section was the best part of the story, I decided to DNF. 
The final nail in the coffin was reading the full plot summary, which has confirmed that trying to finish this book is definitely not worth it. I'm not going to waste 11 more hours on 'meh'.