Eartha Kitt's Catwoman was completely different from Julie Newmar's, but it still worked, because she made it her own. I still say the problem with Astin wasn't that he was different from Gorshin; it was that he was trying too hard to act like Gorshin and was bad at it. He should've done what Kitt did -- embraced his difference from Gorshin and redefined the Riddler to fit his own strengths. That's how you take over a role -- not by being "consistent" with a different person's performance, but by making it so completely your own that nobody's even comparing it to their performance anymore.