Sorry if this post wanders and rambles a bit, but there's a lot in this thread I wanted to respond to. First, while I've read some SK, I'm not what you'd call a die hard fan. He writes some decent stuff, but also some cr*p; he's just too hit or miss for me to want to immediately run out and grab whatever's hit the shelves. That being said I did read the entire Dark Tower saga, and probably will reread it at some point. I don't think it's his best work, but it's definitely not the worst of his I've read.
For those of you who didn't like the ending, tough shinola. It wasn't that he got tired of the series, or the characters, or the readers. The ending was as originally planned and outlined. Granted, the series was only supposed to run 4 or 5 volumes, originally, but this was always the ending he planned. He did often get sidetracked on other projects, and took longer to get back to DT than many fans were happy about, but when the Muse strikes you up side the head, you pay attention and write THAT story or suffer for it.
Of the volumes in Dark Tower, my favorites were the first and last. Those two were the only books of Kings since Carrie that I couldn't put down before finishing. Of his other works, I have yet to finish The Stand. I will never view that has his grand opus.
On the subject of his use of "World as Myth" and placing so many other works of fiction (including a LARGE number of his own), Heinlein wasn't the first to do this (including writing himself into the story as a character) and King won't be the last. I got the impression that King did this as a way to have a little game with his fans (how many books can YOU identify?) and to poke a little fun at himself (which is what Heinlein did in Number of the Beast). Since I'm not a huge fan, this game only bored me and detracted from the story, but I recognized it for what it was and soldiered on, to finally reach a somewhat predictable but pleasing ending to Roland's saga (if that's the right word here). And yes, I, too read DT long before I found Harry Potter, which I also read up to the final (also 7th) volume. Vol 6 pi$$ed me off so much that I have yet to open my copy of The Deathly Hallows, and I don't know when I ever will.
And finally, speaking about Heinlein's use of World as Myth: Poster who proclaimed never to have read Robert Heinlein before, get thee to a library or book store and get a copy of The Moon is a Hash Mistress forthwith. Also grab a copy of Podkayne of Mars (for one of the BEST endings of any novel. While you're at it, pick up a couple of his juveniles, especially Citizen of the Galaxy and Have Space Suit, Will Travel. When you've finished those, you can graduate to Time Enough for Love, Number of the Beast (see WaM reference) and Job: A Comedy of Justice. (Imagine if ALL the world's religions, past and present, were True. Then imagine two people of different faiths fall in love, then die. That's where the story starts.)
A couple of final thoughts and I'll close this rambling diatribe. If they made a movie series of The Dark Tower (even Peter Jackson couldn't do it in one), I wouldn't mind seeing Hugo Weaving as Roland. Who better than him to be humming Beatles tunes while twirling a six gun?
And another thought about King's "game" of King characters in DT. I suppose he might have thought that readers unfamiliar with the books referenced might, after encountering them here, might pick up the other books to compare the characters. If that was part of his strategy, it didn't work in my case.