The Gunslinger is definitely an oddity in Stephen King's list of written works -- it's trippy, cold, and a bit confusing for newcomers to the Dark Tower series. King's typical style is more warm and inviting, comparable to a longtime friend putting his arm around your shoulder and telling you a tale you just gotta hear.
The first novel in the Dark Tower sequence isn't like that, thus it tends to be rather divisive in Stephen King fan communities.
In this book we are introduced to Roland Deschain, the last gunslinger in a world that has "moved on" and his sole mission in life is to reach the Dark Tower. Throughout the book's relatively short length, King fills the reader in a bit at a time on what the Tower is, exactly-- it is, simply, the nexus on which every universe spins. It's the center of....everything. Still, what started Roland on this quest? Hints are dropped, but the reader won't know for sure until the fourth book in the series, Wizard and Glass.
Along the way, Roland meets a couple of people-- Allie in the small town of Tull (which Roland, eventually, is forced to wipe out with his guns in what is just the first of many epic gun-battles in this series) and he soon meets Jake, a boy from our world whom has died and somehow ended up in Roland's mostly-abandoned universe. In addition, we meet the Man in Black, an integral character to every Dark Tower novel.
I can't say too much more because I'd hate to give away anything. Just read it. This is a book that requires patience, however. It gives nothing up easily, nor should it. Still, I am only giving it 3 and a half stars because it's quite obvious King was a young man when he wrote it, but that doesn't mean it's bad. It's just not quite as amazing as the rest of the books in this excellent series. However, it does deserve credit for immediately showing the reader who Roland is and his determination to reach the Tower, as well as doing a fabulous job of transporting one to End-World. I felt I was traveling in the desert and mountains with Roland and, eventually, Jake (my favorite character in this series -- love him!) Upon my third re-read, I finally warmed up to it a little more than I had previously, so there's that. Newcomers to Dark Tower: push yourself through this book. It's worth it.
Long days and and pleasant nights.