In the new preface to this novel, King talks about the germination of this series. One strand of inspiration was J.R.R. Tolkien's Lord of the Rings, even though the two have very little in common. He didn't really know what he wanted to do until another strand of inspiration came: The Good, the Bad, and the Ugly. Whereas Tolkien's fantasy epic finds its inspiration in the mythology of the Anglo-Saxons et al, King's fantasy epic (and it certainly is that) is inspired by the American mythology of the Wild West and the spaghetti western. 
 I have only read the first two installments at this point (a wonderful person gave me this first volume, and I haven't even thanked her yet--gosh I suck sometimes), but it really looks to be not only a fine work, but very much the American epic. Not only does its fantasy element draw from the mythos of the American gunslinger, but it makes frequent forays into modern of the 70s and 80s, and certainly it contains commentary upon the American experience. I enjoyed The Gunslinger and enjoyed the second book, The Drawing of the Three, even more. I haven't read a whole lot of King's other work, but I've liked this series so far and plan to follow it out to its conclusion.