I've seen people debating whether or not TWTTK adds anything to the saga; in my opinion, sadly, it is subtracting from it.
I have many issues with that book (which I liked a lot, by the way - as a nice, quick, enjoyable read) in the context of the DT; here are the main ones:
1. Roland, in the story he is telling, does not look like the man (not a boy any more) who has just come home from Mejis, with everything that happened there. The Mejis part, it seemed to me, was supposed to go a long way towards explaining why Roland became the man we know. Well, now we are back to square one: a young, nice enough boy who doesn't seem to have any particular experience, at least not any that would have malformed him.
2. Now that we can be 100 per cent sure that RF and MB are the same (the note he left was signed by both sets of initials, and Maerlyn refers to RF as "broadcloak"), I really really wish Sai King didn't try so hard to pass Gilead as halcyon society that would be totally prosperous if not for RF. He is behind everything that is wrong there. The next logical step will be to declare him Farson, and all Farson men to be glammed by him.
3. Worst of all, Gabrielle part. What was a truly tragic story is turning into a maudlin piece of unconvincing snot.
Cheap is the word. She is being glossed over the way Gilead is. Moreover, her story stopped making sense.
Hear, hear.