It is all summed up in the handy chart below (source linked to the image). You see, at some point he started referring to his own works a little, and fans thought it was great, all sorts of stuff was happening in the same ‘world’ but ultimately I think it is a sign of staleness. This and yet another ‘Dark Tower’ novel really shows only one thing: none of these are really new ideas, they are tumors on one or two original ideas that were very cool indeed. The very first Dark Tower novel ‘The Gunslinger’ is really quite good, the whole series is far too long. The story is like a radical regenerative from Orson Scott Card’s Treason. It has a lovely arm or face, but it also has 4 legs and three other arms and an extra head growing off its spine… You can chart below to pick stories, anyone you don’t find on this chart like The Green Mile (or only has one outbound connection like The Eyes of the Dragon or Lisey’s Story is perhaps its own story. (Links obviously.. should be obvious… go to Amazon since those three books are actually worth reading. Insomnia doesn’t get a link because it is terrible and I could only manage a few pages before my insomnia was cured forever…)
One final note: the fact that most SK works take place in Maine and even similar places in Maine is not, in itself, any problem. He knows Maine well, and so he writes about the people convincingly….