I tried to read the Dark Tower books, but I had much more fun reading about them.
I have a love/hate relationship with King, and the Dark Tower books pretty much epitomize the hate side. They are King at his most indulgent.
You see, King is a fairly talented writer. He's good with words, and at his best, he tells an effective, spooky, and creative story. He falls into formula sometimes, but even then, there's usually a fun character or premise to cling onto.
The problem is that King *knows* what his strengths are, and he lets it get to his head. He knows he has a gift for making the mundane spooky, and he knows he's one of the more talented writers when it comes to construction and wordsmithing (at least amongst the mainstream). When King is in this indulgent mode, he produces crap. The Dark Tower series, The Stand, It. . .the majority of his library falls into this trap. When he is writing nice little stories like Carrie and The Shining, he does awesome things; when he actively tries to produce great, meaningful works, you get garbage.