The Dark Knight trilogy really wanted to be a realistic, grounded take on the Batman mythos, so they dropped the more fantastical elements of some characters' backstories. Ra's Al Ghul was no longer immortal, Bane didn't have super steroids, the Joker wasn't permanently bleached by chemicals...then there's Two-Face.

I guess they thought acid burns were too unrealistic, so they gave him regular burns...apparently without knowing that burns that severe would be so painful that he wouldn't even be able to remain conscious, much less run around the city on a killing spree. I mean, you can see exposed muscle in some places. There's a line where Gordon says he's rejecting skin grafts, and I remember thinking, "WTF are you talking about? He should be in a medically induced coma, not making healthcare decisions." Half of his body was an open wound; I'm amazed he didn't die of infection 15 minutes after he left the hospital.