On one hand, I understand the disappointment of King fans who hoped for a complete adaptation of all the novels... which would have taken hours of screen time, hundreds of millions of dollars and probably been restricted to a cable channel miniseries. Practically speaking, this film or something like it was the only way to bring the Tower to the big screen. Fans should view this film as either an alternate adaptation or as a sequel, in which Roland finally succeeds at protecting the Tower without all his companions dying.
Bottom line, I enjoyed it.