The best critique I've heard is from people who have a problem with Nolan's directing style, which they claim is a problem across his entire career. And it manifests itself in TDKR in it being so dense with plot and cut with so many scenes that it gives the appearance of being both long and messy. Basically, they think Nolan doesn't let the camera linger enough and doesn't transition between scenes effectively. In TDKR, they think it was cut together too much and in a way that could be confusing and ineffective in driving home the themes.
As I've said, I had no problems following the plot. And I've enjoyed all of Nolan's films, both visually and plot-wise. So as a personal preference I don't really have a problem with Nolan's directing style. I quite enjoy it. But unlike with some people's specific problems with the plot, I can kind of see the merit of this criticism. And I think the issue they are talking about is why I had to watch both TDK and TDKR a second time to form a firm opinion about the film. After seeing TDK, the only thing I knew was that Ledger was incredible. And after seeing TDKR the only thing I knew was that I loved the ending.
Perhaps I couldn't form a coherent opinion about the movie as a whole because Nolan's direction isn't the most coherent style, at least upon first viewing. Indeed, I think Nolan would acknowledge this himself, at least with movies like Inception and The Prestige. His Batman films are more straightforward than his other films. But they are still packed with a lot of scenes and a lot of plot. So while this could be a personal preference type thing that may not have a answer, I'd encourage people to watch the movie a second time. I think you'll get a better sense of what Nolan is trying to do.
I wrote this post back in December of last year about the idea of having Robin in TDKR. Here's what I said about the idea:
If Nolan were to include Robin in TDKR I don't think it will be in an explicit manner. Meaning, I don't think we will see a young man in red and yellow tights fighting alongside Batman. If we do see Robin, I think it will be him as just another young man who happens to come into contact with Batman or one of the villains in some manner. And I think the most that will be mentioned of him is something in passing, kind of like how Fox mentioned cats when talking about the new armor in TDK.
Or another way I can see it is him being part of that group of guys who dressed as Batman early in TDK to try and help the real Batman, those guys in the hockey pads. Perhaps they make another appearance and instead of sucking one of them is really good at fighting the bad guys. And perhaps Batman takes notice and says something like, "Not bad kid. Maybe you should be my sidekick." after the young man takes out a villain before Batman can get to him.
I wasn't too terribly far off. I'm glad Nolan decided to put Robin in the film. I thought it worked perfectly. And listening to people familiar with Robin in the comics, it seems like Nolan kind of mashed together the three main Robins in order to make John Blake. My take was that Blake was kind of being Robin throughout the whole movie.
He was a cop who had a past that mirrored Bruce Wayne's, one that gave him that same drive to enact justice on Gotham's criminals. He used his natural detective skills throughout the movie, to figure out who Batman is and to figure out what Bane was doing with the cement. And he had the will to act. He wasn't afraid to stand up to Bane's men. So in the last scene when he rises up on Batman's platform he is literally becoming Batman.
Just like Batman began when he jumped off the building in Batman Begins and Batman became the Dark Knight when he took the fall for Dent and rode off into the night in TDK, the Dark Knight rose again when Blake/Robin stepped onto that platform.