While it's sad seeing those who defined the roles leave them, there were parts of Sorkin's performance in Arkham Asylem that were not quite as satisfying. Particularly when she rerecorded the dialogue from "Mad Love", an episode I always loved her performance in, for her tapes in the game. The episode really sold the idea to me that Harley was a genuine psychiatrist before her corruption. The way she contrasted the persona of Harleen Quinzel to Harley Quinn just... enticed me. It did a far better job than the original comic (mostly by removing the references to her... proclivities in college) in convincing me that her fall was sincere and significant. But in the tapes, it was flat. There was no change, no real effort, no soul in it. While I appreciated the reference, I felt that the lackluster performance lost something that gave the previous rendition power. I admit I don't know how much of this was Sorkin and how much was her direction, but something was missing in that instance and I find it hard to ignore.
I have always liked Tara Strong as a voice actress and I'm certain she can carry the role for this game as well as anyone can.
(Of course, no one can ever truly replace Mark Hamil as Joker)