Read: The Road to the Dark Tower, Ben Vincent.
This relatively uninspired book provides a guide to Stephen King’s Dark Tower series, with all the usual things you’d expect: a chapter summarizing each of the seven books in the series, a chapter on influences, a chapter on the relationship of the series to King’s other work. This latter is probably the most useful piece of the book, since the Dark Tower series is highly meta-fictional and refers to many of King’s other books. However, you can find an equally good reference (if not better) on the web.
Really, The Road to the Dark Tower is workmanlike but not fantastic. The main reason to read this is if you’re a major fan of the Dark Tower series, which you should be.
I’m not kidding, by the way: I don’t care if you think Stephen King is a hack (he’s not) or burned-out (he’s not) or for the illiterate (he’s not). Yes, he’s written some crap, but The Dark Tower series is a brilliant work. As a writer, King is an extraordinary craftsman, and in this series he’s finally given himself material that lives up to his abilities. King’s skill at evoking character through concrete detail is unparalleled, as is his ability to transform the ordinary into the stuff of dreams and nightmares. In The Dark Tower he finally creates an epic, genre-spanning work that incorporates fantasy, Western, horror and more into the single best evocation of a fantastic America I’ve ever seen.
No, the series isn’t perfect. For one thing, volume one doesn’t quite manage to grab you the way the rest of the series will - bad news for new readers, who should just stick it out until volume two! But even with its flaws, the series’ stunning originality puts the competition to shame. (The books make Gaiman’s American Gods, just for example, look more than a little anemic.) King manages to create a fantastic universe that actually reflects American culture and history, without grounding his imagination completely in the modern world.
One warning, though: the series clocks in at well over two thousand pages, and dense ones. It took me almost two weeks to get through the whole thing, and I read fast! Nevertheless, King’s magnum opus is well worth the time it’ll take you to get through it. It’s definitely on my “favorite series of all time” list, and if you read it it’ll likely make it onto yours, too.