The first half was great and the changes with how they made him Two Face worked, but he's a villain who deserves more than being an after thought in the Joker movie. And then killing him at the end in that way was lame.
I disagree. The transformation of Harvey Dent was the pivotal moment of the whole thing. The entire film was Bruce's quest to see Harvey Dent take over as the crusader for justice, and Joker's plan to corrupt Gotham's "white knight". Dent/Two Face is the most important character in the whole thing.