As a recent review said, this really is the pinnacle of the series. Unlike that person and many others, I wouldn't quite say it's downhill from here as personally I loved the way the series ended. But then that's another book, another day and another review.
Wizard and Glass is mostly set in the past, telling a story of Roland's days before his quest. After the cliff-hanger is resolved, Roland decides it's about time he told them more about the beginnings of his quest and as the day ends, time slows as he's able to tell his whole story in one "night". Once the tale is told they have an interesting confrontation with the Man in Black and then head off again along the beam. What's amazing about this book however is the tale in between. The rest are really book-ends. At the start, the conflict had to be resolved and at the end we had to be brought back onto their quest, back to the present.
Some people criticise spending a whole book in the past, but then, by now don't they care a lot about Roland? I certainly did and I wanted to know more about him. I admit I felt daunted by the prospect of such a long tale, but when it contains the best storytelling in the series that soon fades. This has drama, emotion, character development and an intriguing plot. It's a fully resolved and extremely well-told tale. The ending brought tears to my eyes, and any tale that can do that can't be anything but well-told.
We also get to find out a bit more about Alain and Cuthbert, which is really important in understanding who Roland is. And we get to see Roland, more or less at his best. The plan of three gunslingers being carried out with skill and precision, though not perfectly, for nothing ever goes perfectly.
My own words aren't really adequate to describe how good this book is, so I'll leave it there, just adding that if you're thinking of reading these books then you're in for a treat when you get to the start of Wizard and Glass.