The Dark Tower series is tremendous, and well worth reading. It's my opinion that, much like your average sandwich, the best parts are found in books 2-6, as book 1 was somewhat uninspiring and book 7 was, while having its moments, overall a disappointment w/ some very questionable plot and character/enemy choices, IMO. Don't get me wrong, it ended the only way I thought it reasonably could've and should've, at least. But, the journey to reach the Dark Tower was simply amazing and I strongly recommend reading it. I was genuinely sad when it was over.
And for those mad that there's no "final" conclusion, let's just say I read a very interesting theory on another message board that says that final conclusion you guys want is actually described in brief but precise detail in the book already, you guys just didn't recognize it. I personally think that theory is brilliant and correct. Go find it yourself, I'm not saying where it is.
On another note, while I enjoyed The Stand, I read it after I read the DT series, so Flagg didn't seem nearly as dangerous or mysterious, and that kinda spoiled the book for me. My top three standalone books from King are probably It, Desperation, and Black House.