Re Room 237 and The Shining, here's something I posted somewhere else that I think answers why some of the things in the movie that baffled Josh and Adam are in it, and generally touches on the question of what the movies is "about" without, hopefully, going to Room 237 extremes. For me, it's very much of a piece with Kubrick's other work, and as Frederic Raphael said, all of Kubrick's movies are about the Holocaust on some level:
Certainly one of the themes of Kubrick's entire life and career is informed by the Holocaust and the idea that, beneath a very thin veneer of civilization, we are apes with sticks beating each other and no better than that. For me the big Holocaust reference is the one hardly mentioned here: who is Jack Torrence but a failed artist turned apparatchik who finds his purpose in a murderous bigger cause than himself and can hardly be more eager to please it with whatever violence it asks of him? Hmm, failed artist... who does that remind us of?
Likewise I think the Native American allusions, though in no way the subject of the film, are there to remind us that 10 minutes before this fine, dignified hotel was built, people were killing each other with hatchets on the same spot. That's the universe according to Kubrick. You can't kill in here, this is the war room!
And finally, I think there are definite hints, per Rob Ager, that the story is "about" (I use that word cautiously) child abuse, possibly sexual. (I mean, a teddy bear is performing sex on a man, and there's a boy with a teddy bear, how much more do you want it spelled out?) Child abuse is often a generation after generation cycle, and though there's no way to reconcile all the timelines and say exactly when which Mr. Grady was there and so on, there is kind of a feeling that both Jack and Danny are caught in the same endless cycle, but Danny, who doesn't repress his shining the way his dad evidently has, is ultimately smart enough to find his way out of it. One of the things that the movie is "about" is that Danny is, in the end, better than his father. Jack seems a damaged person in part because he's repressed his own ability to shine. He denies to himself that he has the ability-- which makes him more susceptible to seduction by the hotel, I think. Danny on the other hand is comfortable in his and uses it when he needs to, and that's why he is able to escape the cycle his own (perhaps abused?) father is stuck in.
Likewise some of the visual clues that Rob Ager points to are unmistakable-- Shelley Duvall DOES dress like Goofy and the elevator signs do match the Teddy Bear and so on. Maybe even the copy of Playgirl... I mean, Kubrick didn't do anything randomly, but some of them may be no more than jokes on the set.
But let's stop there. Is there an entire deep subtext that took 30 years to unwind? No, I think most of these things were sensed by people, if not exactly articulated, early on, and are found in other Kubrick movies all along. Jack with a hatchet is scarcely different from Alex with a cane or an ape with a bone or Barry Lyndon suddenly snapping and attacking Lord Bullingdon in public. Kubrick's themes are not mysterious; they're merely subtly developed.
A few other notes:
1) There were a number of adult horror movies in the 60s in which you were left to wonder if it was all in the head (i.e. The Innocents) The Shining plays to our expectations with that; there's nothing that is supernatural and requires the help of ghosts to happen-- until there is.
2) Saying Kubrick didn't really care about the material or suspense misses how beautifully he sets up all the pieces of the puzzle. As a pure suspense film everything (like Danny and Halloran's ability to communicate when there's no other form of communication) is put in place very neatly. He wasn't slacking in that regard, it's as meticulous as anything else in the film.