This series to me is very unique. Usually (to me) Stephen King's strength is that his characters seem so real... like someone you can find just down the street or even yourself... but placed into extraordinary situations.
In this case though, the protagonist, Roland (I think) the gunslinger is definitely something else altogether. Definitely not an ordinary chap. The series is also his magnum opus. If you've not read much of his other works... well, there are a number of tie-ins and allusions to this Dark Tower series. The Dark Tower universe is meant to be the central hub that connects many of the earlier works of Stephen King. (If memory serves), the end of Insomnia, for example alludes to Roland.
Haha... sorry if you already knew all that. Just thought you'd like to know.