So there are series of movies called "Trilogies", right? It entails three movies that are connected, with similar story/character arcs.
There are trilogies that start out great, then have movie just as great or better, and then completely bomb in the third film (i.e. The Godfather, Sam Raimi's Spider-man)
Then there are trilogies that end nicely (i.e. the original Star Wars, Toy Story)
The Dark Knight trilogy is a complete, masterful trilogy that contains superb material that sets the bar ridiculously high for not the superhero/comic book genre, but in cinema in general.
Congratulations, Mr. Nolan. You have developed one of the greatest trilogies of all time. And goddamn you for ending it on amazing note.