Did you read the original The Gunslinger from 20+ years ago, or the updated The Gunslinger that was re-released a few years ago?
Anyway, the series was written over such a long period of King's career that the writing style changes throughout the series. Book 1 is different than 2 and 3...and I'll add 4 to that group as well. And then there's the last 3 books, 5, 6 and 7, which are waaaaaay different in style.
My favorite book is definitely 4, Wizards and Glass. The last 3 books aren't as good as the first 4, but still worth reading. The Dark Tower was my gateway to reading other King novels.
BTW, no spoilers means NO SPOILERS people. Even alluding to them! You know whose post I'm talking about...