I liked the ending. Up until that point, I felt that, while Ezio had the all the trappings of a great hero, there was something about him that didn't feel quite right; the pacing of his character development just felt off. By revealing that his purpose in the grand scheme of things is simply to act as a vessel for Desmond, it alleviates the pressure for him to be a well-developed hero. It also makes him a little more interesting in a roundabout kind of way; can you imagine having to live the rest of your life knowing you serve a greater purpose, but never understanding what the purpose is?