I do like multiple choice endings, but my problem with the tower is that he doesn't really give you one at all.Many of SK stories are open- ended, leaving it up to the reader to decide. A conclusion , in my opinion, is not always necessary. Without one, it leads to lingering questions for the reader. The ending of the DT kept the authenticity of Roland's quest.
When Roland is transported back to the beginning of the story, doomed to repeat the whole tale again, except this time with the horn of Eld, so it is hinted at that with the end things might be different, although, we never get to find out what differences await Roland at the top, this is my problem with it.