There are good ways to reform a character, and bad ways. This has been most obvious in the recent episodes of "The Venture Bros.", where Sergeant Hatred went from being a one-off joke character based on a silly incident the writers witnessed at a cafe with a sexual deviant to one of the show's most tragically compelling characters. Like Dini's Riddler, he's built for comedy; but the comedy comes laced with depth, the depth of his need to get beyond his numerous addictions, deal with his failed marriage, become a moral person and above all build up his self-respect.
The key thing is: depth. Dini's Riddler has been entirely about him being an unrepentant arse, doing really horrible and stupid things in order to get what he wants without ever feeling bad about it, and was lent some actual character in books written by other people - "Gotham underground" and "Trinity". Sgt. Hatred, on the other hand, can be the butt of ten hundred pedophilia jokes, but he'll still be my new favourite character of the series because I know that that's not all there is to him. Hatred's character reformation took, and is still taking, dozens of episodes to come through; the Riddler's could be summed up in one sentence.
In the annals of the Bat-History, Dini's Riddler - like most of his run - is a mere blip, a brief development that went nowhere and did nothing. Long may it stay that way.
And, ugh, don't remind me of that upcoming Zee series. I'm so looking forward to seeing Dini express all of the fetishes he associates with his wife through one of the supposedly most powerful magical beings in the DCU...