This is the book which first catapults us into Roland's world, introducing us to the enigmatic gunslinger and his rather strange world.
This revised edition was published in 2003, to coincide with the release of the final books in the Dark Tower series. In his introduction, King compares this to the expanded edition of The Stand, only on a smaller scale. Generally, a few alterations have been made so that the book, originally published back in 1982, ties in more nicely with the later books in the series. I own, but have yet to get around to reading, the book in its original form so as yet I can't judge as to whether or not the revised edition was necessary.
The most common complaint I hear about this book is that people have found it boring. It seems a strange complaint to make; here we are, introduced to this compelling and mysterious character, a gunslinger capable of wiping out the entire population of a small town in just one afternoon, yet you can sense that he is inherently good. You immediately want to know more about this character, why he seems so dead set on catching up to this Man in Black, and why an eleven-year-old boy from New York City could end up in the middle of the desert in another world. With so much to think about, it seems odd to think that a person could get bored reading this.
If you are familiar with King's other work, then this book will seem a little strange at first. Unlike the other books in the series, it doesn't read quite like a Stephen King novel. Perhaps because it was one of the first books he wrote, or perhaps because its protagonist is a character who has never heard of America, let alone the state of Maine. A Clint Eastwood-esque gunslinger who grew up in a castle and whose coming of age was marked by a bloody fight with his teacher, Cort. In fact, for the first portion of the book we're not even told the gunslinger's name. That, along with the title of the novel, is symbolic of how mysterious this character is. We read an entire novel about him and come away realizing that we actually know very little about him. Throughout the whole series there's something enigmatic and distant about Roland. By the end of book seven we've come to care for him deeply, yet we still don't really know him.
A point to note is that you should definitely re-read this after completing the series as you'll be amazed at the little references you missed first time around (which I presume do not exist in the original text). I was also quite delighted to find a Watership Down reference in there too.
For me, The Gunslinger is a fantastic introduction to the Dark Tower series and I would highly recommend it to everyone.