The dark tower series is one of his best IMO. Unfortunate he ended the series earlier than planned... Was supposed to be quite a few books longer but I remember reading (and I could be remembering wrong) in the foreward to one of his books that the weight of people sending him letters such as "I'm terminally ill, i was hoping you could tell me how it ends before I pass" and all the other contact he got led him to cut it a bit short. That said, I think it's his best work.