In my opinion Bruce Timm's cartoons gave us definative versions of not only the characters, like Batman, Joker, and others, but also their voices.
When I see a character done differently it seems wrong to me.
I can't imagin anyone else as the voice of Batman but Kevin Conroy (spelling?), anyone as the voice of Joker but Mark Hammil, Or the guy from Night Court, can't remember his name, as the voice of Two-Face, Clancy Brown as the voice of Lex Luther, the voice actor who did Brainiac, likewise with the Question on JLU, Darksaide and Mongul, Knightwing, same goes with almost every other character's voice.
When I am reading a DC comic I usually imagin those voices.
It would have been great if he could have animated the entire Doomsday story. including the fight between Doomsday and every other DC superhero like Blue Beetle, Fire and Ice, Guy Gardner, among others.
But I know that would make for too long a movie and they probably weren't allowed the rights to any of those characters.
Great cartoons.