This is the third book in Stephen King's Dark Tower series, and it's the one where King really finds his flow. Whereas before this the series had suffered slightly from unsure writing and the feel of an author finding his feet with his characters and plotlines, this entry in the series is assured and authoritative.
Our main character, Roland, and his "Ka Tet" (fate-bound group of companions) set off once more on their journey towards the Dark Tower. This is a tale of travel, and includes more twixt-world hopping, a giant bear, a derelict city, and culminates with an insane train.
If that all sounds a bit mad, that's because it is, but its also excellently written and gripping. This novel was written with a purpose, and it's great to get wrapped up in the exciterment and enthusiasm that Kind clearly felt when he was writing it.
If you've made it this far towards the Dark Tower, then odds are you're going all the way to the end.
PS: It's worth noting that these recent editions of the paperbacks come with a foreword and "thus-far-synopsis" by King, where he sharesd his inspirations for the Dark Tower books and some of his thoughts on writing, the universe and everything. They make for intriguing reading, and certainly improve the novels as a whole.