The dark tower series is a series of cliffhangers. With no real direction and a scanty outline Stephen can not paint himself into a corner. As with any dream (nightmare) you just change the rules if you get stuck with some logic. And this is what it is, just one long dream. It has all the elements of Stephen King including his potty mouth.
Do not try to compare this loosely jointed series of encounters with works such as of J.R.R. Tolkien, Robert Jordan, and George Lucas, as they have no resemblance to the Joseph Campbell myth of someone challenged to become more than they are. This animal is in its own purely fantasy (don't look for depth) project. I say project because it is ongoing with out a clear stopping point in mind. If you look at it this way then it can be a "five star" in its category.
"The Gunslinger" is over before it gets started no time to form an opinion.
"The Drawing of the Three" twice as long as the previous, leaves you with a dislike for lobster.
"The Waste Lands" twice as long as the previous, leave you with a dislike for Amtrak.
By now you have no opinion, dislike eating lobster on Amtrak, and can not wait for the next installment (Wizard and glass.)