Arnold Etchison is a regular old crazy person. A serial killer. The twist is that his victims are people he's related to, believing that he gains their strength when he kills them. I don't think he eats their brains or hearts or anything, but there's a limit to the gore you can have in all-ages Batman comics, so I bet they at least wanted him to. While acting as Batman, Jean-Paul Valley allowed Abattoir to fall to his death (which became part of the reason for Bruce Wayne to become Batman again). Etchison came back as a ghost in a later Batman storyline that's probably best forgotten.
Pros: No supernatural stuff (not counting the ghost part).
Cons: He's not all that interesting.
How I'd do it: You don't really have to change the character, except come up with some way for the audience to be frightened by him.
Casting Guesses: James Spader. I have no idea why, but I feel like he'd be a good crazy Abattoir.
Verdict: Nah. If you're going to have a regular crazy murderer, Zsasz is the best choice.
After The Scarecrow, Ra's Al Ghul, The Joker, and Two-Face, who should be Batman's next enemy in the Batman Begins/The Dark Knight series? Well, as of now we know that Tom Hardy will play Bane and Anne Hathaway will play Catwoman.
Check out the master list for all the villains covered. I've pretty much run out by now. Obviously, there are more Batman villains, but not any of significance that I know of. As of February 2009, no one is confirmed as a villain. Not the Johnny Depp Riddler, not Phillip Seymour Hoffman Penguin, nobody.