Let me start this editorial by saying that I am a huge fan of this trilogy. I think that each installment is brilliant, and an example of how to make a great film.
In my opinion, here is what was missing: we needed this to be an anthology, not a trilogy. The Dark Knight was the definitive Batman film for me. It teased that Batman and the Joker will be squaring off toe-to-toe for years, it finally put Gordon in the commissioner role, and had so much going on that made it great.
So then we head to The Dark Knight Rises, and he just quit? A third film with any villain, preferably Riddler or a return of Two-Face, would have provided a greater exposition to lead to the fourth film. All in all, Bruce was Batman for maybe 2 years. That's not long enough to believe that he had been worn down the way he was in TDKR. I know he was out every night "working," but he needed that fourth film to really get the feel that he had been Batman for a long time.
TDKR was a great film in my opinion, and it had a great ending. I personally would have liked to see one more outing for this version of the Batman. What do you think? Sound off.