I've always shot down the assertion it wasn't a Batman movie, or Batman was irrelevant, or he didn't get any development, or any cool scenes, or any of the other ridiculous criticisms haters made against it.
He learns what his limits are, what Batman can endure both personally and symbolically, he learns about the nature of criminals like the Joker (and actually learns from his encounter with the Joker to face him again, like by the finale he sees right through the Prewitt building set up as not being what it seems - "It's not that simple. With the Joker it never is"). And yes, his selfless sacrifice at the end when he learns Batman can be what ever Gotham needs him to be. Compare that to Bruce at the beginning of the movie who arrogantly thinks Batman has no limits. Bruce's growth in this movie was learning what they are, what he can and cannot endure, and learning about the terrible nature of freaks like the Joker whom are a reaction to his presence in Gotham just like the copycats. TDK was a real eye opener for Bruce and what exactly the effects of Batman are on himself and on Gotham.
He has tons of great scenes. His take down of Scarecrow and the imposter Batmen in the parking garage. Abducting Lau from China. Kicking ass in Maroni's club and dropping Maroni off the fire escape. The whole Joker truck chase he was bad ass with many cool moments like taking out the garbage truck, birth of the Bat-Pod, and flipping over Joker's truck. The Prewitt building scene is probably the coolest Batman has ever been on film taking out two SWAT teams, Joker's men, and protecting the hostages, too.
There was a great mix of funny and serious Bruce Wayne scenes, too, like the aftermath of Rachel's death where he's quietly mourning her with Alfred - they did a great mirror image of the childhood Bruce mourning his parents there where Alfred comes in, says something about food, Bruce ignores him, Alfred says "Very well" and goes to leave and then Bruce calls him back. All the playboy Bruce stuff was gold. Seeing Bruce use the daylight hours effectively as Bruce by staking out Loeb's funeral, and following Gordon and Reese and having Alfred run a check on all the Cops he recognizes (love that Bruce knows many of the Cops by name) etc.
Bale's performance, and the character in the movie, is often underrated. Take him out of the movie and there is no movie. Everything that happens in it is because of Batman and his presence in Gotham. It's basically an examination of the consequences of Batman on Gotham.