I can understand why King himself doesn't like this adaption

Unhinged...from the beginning?

Totally disagree. Not quite normal, distracted etc but hardly unhinged, not until further into the movie.

It's clearly a gradual descent into madness.

That's just Jack Nicolson being Jack Nicolson. He always seems unhinged, even when he's supposed to be playing it straight.

Some actors have such charismatic or distinct personalities that it flavours every performance they give.

Christoper Walken is another example of this phenomenon.

Sometimes it can reach self-parody. Al Pacino went through a phase where he was always wild-eyed and shouting regardless of the role. He eventually dialed it back... maybe on the advice of directors?

That's exactly what King was saying in one of his interviews. Also: ...King also viewed the casting of Nicholson as a mistake, arguing it would result in a rapid realization among audiences that Jack would ultimately go mad, due to Nicholson's famous identification with the character of McMurphy in One Flew Over the Cuckoo's Nest (1975). King had suggested that a more “everyman”-like actor such as Jon Voight, Christopher Reeve, or Michael Moriarty play the role, so that Jack's subsequent descent into madness would be more unnerving.[79]

Kubrick himself stated that it was his intention not starting with a "normal" guy. He had no interest in a "sane guy goes mad" story. His vision was to show a man on "the edge" from the beginning and his struggle not to go over it. So for him the casting choice made sense.

I hadn't seen the movie since I was a kid sneaking horror movies, so I decided to read the book and then watch the movie again. And the movie is good, but as an adaptation it's bad.

As for Jack Torrance, the thing I hated most about him was that it never showed any love between him and his son (in fact they rarely had any scenes together until towards the end). He tells him once he loves him, but that was when he was holding him and already gone fairly crazy. In the book he fought the things going on in his mind because of his love for his family, especially Danny. In the movie it seemed like he went 0-60 right away and never showed any empathy towards them at all.

He seems a little off but hardly unhinged. I like the book but I love the movie. King was a talented writer but also an idiot.

IMHO Kubrick was right and King was wrong, although I can see why King feels the way he does because the Jack of the book was largely based on King himself. Of course he feels protective of the character!

I understand the book was basically about a family being threatened by supernatural forces, but Kubrich was right - a parent going murderously crazy is FAR more frightening than any external threat, even if it's supernatural. Kubrick got to our inner core, the feelings of being a small child who has no way to cope with an angry parent, the helplessness of having absolutely no alternative but to cling to the parent even if they're being horrible, that's a feeling that's always deep in there somewhere. So Kubrick did what King has never IMHO done, and that's to dig terror out of the universal subconscious.

And he set it up so neatly, with the opening scenes showing an obviously troubled father and a mother in denial, and us sitting there thinking that THESE people are going to go spend six months snowbound????

I watched this for the first time in quite a few years recently. But after watching it, I read a summary of the book with spoilers. Frankly the book's ending is more epic. In the book, Hallorann actually survives and helps Danny and Wendy blow up the hotel so that the spirits can't haunt there anymore. Then they all escape together. The movie's ending was not as epic with Jack getting lost in the garden maze and Danny and his mom simply escaping on the snow vehicle. I should watch the miniseries that was done by King a few years ago which may have that epic ending in it. I also want to see the sequel done a few years ago.