With BTAS, it just always felt to me like they softened the character up too much for the kids.
Compared to the comics of the time, certainly. But compared to previous screen incarnations of the Joker, he was about as malevolent as they came, at least within what FOX censorship allowed (they were able to take it further in Mask of the Phantasm
, the revival on the WB, and Justice League
on Cartoon Network, all of which were less censored). I'd say he was about on a par with the Joker of the '70s comics, when Denny O'Neil turned him into a murderous character again but the overall tenor of the comics wasn't as dark and brutal as it became post-Miller. B:TAS probably owes the most to that era of Batman's history. (One of the most memorable Joker episodes of B:TAS, "The Laughing Fish," is an adaptation of two seminal Joker stories from the '70s comics; most of it is based on the Steve Englehart/Marshall Rogers story of the same name (which in turn was a remake of sorts of the Joker's debut story from 1940), but the last act was taken from O'Neil's "The Joker's Five-Way Revenge," the
story that reinvented the Joker as a cold-blooded killer after a couple of decades as a more comical figure.)
I'm surprised to hear these criticisms of Hamill's Joker, when for a very long time I heard him pretty much universally praised as the definitive Joker of all time. I wonder if Heath Ledger has changed people's view of what the Joker should be, so that people now want something more subtle and controlled. Certainly both DiMaggio's and Spiner's versions of the Joker in recent animated productions have been more in the Ledger vein (or the Ledger domain, heh heh). The one post-TDK Joker that's still more raucous and wacky is Jeff Bennett's in The Brave and the Bold
-- which probably owes something to Larry Storch's and Lennie Weinrib's interpretations of the Joker in the '60s and '70s cartoons.