Wizard and Glass was my favorite of the series too, really a great book. Obviously one needs to finish the series if they got this far, but the remaining books were pretty bad in my opinion. I recall King saying he was contemplating retirement due to the pain and such relating from when he was hit by a car a while back, but he wanted to finish the dark tower series as he felt it was his, I can't recall his exact words but something about being the most important story. If I recall the last three books (or was it four) were released over the course of like 18 months, and I feel they were not that great and this was probably due to a rushed pace to finish them. But I am sure he wanted the relief of being done too, he often talked about how it was the hardest stories to write for him. I think I still have the series at my parents house, I should pick them up next time I am there.