I just wish they had called the Joseph Gordon Levitt character Dick Grayson and called it a day. From what I can tell, the only reason they didn't was to put in that "Robin" surprise at the end to elicit cheers from the audience (which it did), but Nolan is usually better than that.
Dick Grayson was an orphan who had a deep connection to Bruce Wayne (the reason he took up the costume in the first place is because they saw a similarity in themselves). He also later became a cop and took up the name of Batman at least twice in the 70 year history of the comics.
As a comic book fan, part of the appeal of these comic book movies is seeing your favorite characters up on the big screen and Dick Grayson is one of my favorite comic book characters of all time. And on top of it, I thought it was a perfect portrayal of a Robin type character in terms of the Nolan-verse.
Otherwise I loved the movie. As someone who thought that Nolan avoided the comics more than I'd like, I found this to be a pleasant surprise bringing in elements from a lot of comic book stories such as Officer Down, No Man's Land and probably most obvious Knightfall. And there was even a little bit of Morrison in there with Talia being the real bad guy as per the current Leviathan story and someone taking over as Batman. I also loved the updating of the Lazarus Pit.
While it wasn't a perfect movie, I thought it was a very fitting ending to the series. And I think that this could stand as the most consistently good trilogy of all time. And the Dick Grayson/John Blake thing stands as my only major gripe.