i just finished the extra book king wrote after the DT series was over – “wind through the keyhole” – that could be nested between books 4 and 5. it confirmed some theories i had at the end of the DT series. don’t read the jump if you are planning on reading the series.

at the END of the series, roland is thrust back into the beginning, but this time with the horn (which should signal this would be the last time through). we get the impression that he’s been down this road many, many times before. (ka is a wheel! get it? it’s circular.)
but, i had surmised that perhaps roland kept getting ka’d back to the beginning because he still felt guilty about killing his mother, and that he still needed to work on forgiving himself. (of course i didn’t put this in writing in any place after i finished; i just thought about it.) since he had gotten the horn this time through, he had forgiven himself, his mother, etc. for all the mess that happened.
after finishing the supplementary book, i think this is a pretty accurate theory. roland tells a story during the end of which he received a post-humous letter from his mother telling him she forgives his for all and would he forgive her? and at the end of the book, susannah asks if he had. after much contemplation, he lit up and said yes. like it had suddenly come to him that yes, yes he does forgive her (during the course of which he would have forgiven himself).
further proof that the ENDING of DT DOESN’T SUCK!!! it even makes it MORE likeable!