They treated the whole Khan thing way too comic book like. Khan is not the Joker, who is a constant enemy of Batman. Khan is just one of many antagonists, and the crew had to face a lot more problems and adventures.
They confronted V'Ger, the Whale Probe and stopped a Klingon-Federation conspiracy. All that was far more dangerous than Khan ever could haved dreamed of being.
Totally agree. I never understood how this myth got started that Khan is Trek's defining villain, the Joker to Kirk's Batman. He was villain of the week in one episode and brought back in one movie. Yes, it was the most popular movie, but it is only one movie. Honestly, I would have thought the Klingons would have been more recognizable and the ones with more merit to be called Trek's "defining villains" and STID should have been about them.