The Dark Knight and The Empire Strikes Back have a few things in common. First of all, they are the second film of a trilogy. Second, they are the most loved films of their trilogies. I personally have a theory on why the second film could easily be the most well liked film of a trilogy. But first, there are a few points to remember.
This theory best applies if there is an over arcing story to the trilogy. Second, this is not a hard fast rule. Various factors can affect for good each film is. The Star Wars prequels weren't super great and Revenge of the Sith was just lucky to be the best one. If the prequels were done well, Revenge of the Sith might have been the best prequel. Third, there is a level of subjectivity when evaluating film. I personally have a bias towards a good climax, so my personal bias towards a third film.
To understand why the second film is often the most well liked, you have to understand why three many film series have three films. Any story has a three act structure. This includes a novel or movie. The beginning sets everything up. The middle advances the plot. The end solves the problem and ties up loose ends. Another way to look at it as one of two cycles. There is the cycle of introduction, rise, fall. The other possibility is the cycle of introduction, fall, rise.
So here is how this translates into a trilogy? The first film introduces the characters. The second film has the most plot development and character development. It moves to set everything up for the final film. The final film just ties up loose ends and shows how the hero's journey ends.
A New Hope introduces Luke. The Empire Strikes Back develops him through his training and confrontation with Vader. The revelation of Vader as Luke's father and Luke's defeat set up for Return of the Jedi. Return of the Jedi shows that Luke becomes a Jedi, chooses good and redeems his father.
Batman Begins sets up that Bruce Wayne wants to be a symbol of good for Gotham. The Dark Knight takes a deep look into his character. It sets up The Dark Knight Rises by having Batman take the blame for crimes he did not commit. The Dark Knight Rises shows Bruce moving on and Batman becoming that symbol of good.
In all, the second film often has the most story and character depth. Please note that this is not a hard core rule. This often applies only if there is an arc spread across all three films. The consequences is that the third film can be underrated because it gets compared to the second film.
