The only people to do a cool, interesting take on him was Dini and Timm. And even then, the character was barely in the series. He's the definition of camp.
Actually, if you look at the source material, he's not. Due to Frank Gorshin's popular version of the character (which later influenced Jim Carrey), the Riddler has seemed to be camp. The reason he was rarely used in BTAS was because the producers had problems coming up with a story that wasn't that complicated and could fit in a 22 minute time period.