I thought the devlopment of Two-Face in this movie is very, very well done. If anything that's a "dislike" about TDK on two fronts. On the first front there's no "development" of The Joker's evil. He just is, and granted Heath Ledger does a great job of it, but we watch Harvey's change over from a brillant and stable DA, to his near break-down with the pyscho caputred at the parade/memorial for the old Comissioner and finally to his collapse after getting half his face burned off.
It's a shame that at this point it doesn't look likely we'll see Dent return as his evil was really well built up in this movie.