I enjoyed the feel of the first one, but then again I enjoy the grittier feel of early SK stuff, as well as the Bachman Books. It has more of a western feel, which is appealing in its own right.
To me the series is worth a read, even if the final ending makes you want to scream. The 5th book, Wolves of the Calla
was my favorite. I enjoyed the development Mid-World's mythology and the characters themselves. Detail-wise, Stephen King didn't know much about guns when he first created Roland and his revolvers. That might bother some hardcore gun nuts, but ends up explained away as that being part of The Gunslinger's world, not ours.
Some of the graphic novels are kind of cool once you read the series, but not necessary. If I can find them used for an affordable price, I'll buy them. I read comics way too fast for it to be feasible entertainment.
Overall the series is better than most of his "newer" (post-accident) books. Duma Key
is another exception in my opinion, and 11/22/63
was ok but not what you expect from his writing.