Bale's performance in TDK is solid. He brings the character to life, he convincingly emotes and conveys Bruce's/Batman's struggles, and in no way gives a good performance.
I think the perception of a "poor" performance comes from Dent being the protagonist of the film, rather than Bruce/Batman. This was a deliberate choice on Nolan's part (and he explicitly says so in the Art and Making of The Dark Knight Trilogy book). Bruce does have a character arc, but it's shorter and more subtle than Dent's. Hence, Bale's acting doesn't attract the attention that Eckhart's (or Ledger's) does.
gaspernoe wrote:Of all the the things that can be praised about this truly wonderful movie, Bale's performance isn't one of them. I didn't notice it at first when I first saw TDK in theaters because I was so immersed by the story and Ledger's epic performance. But on repeat viewings I noticed how stilted and one dimensional his performance. It's always been a conundrum for me, especially when Christian Bale is a pretty good actor. Even without Ledger's overshadowing performance Bale looked like a shell in TDK. He wasn't nearly as good as he was in TDKR and even BB.