Superheroes, almost since day one, have always been featured in media outside of the comics they originated from. Let's face it, we, as comic fans, find them to be very interesting, most of the time and of course, would gravitate towards anything related to them. They could make Spider-Man toilet paper and about half of us would buy it. All toilet paper aside, superheroes have been featured in animation since the 40s.
The earliest example of this was Superman, whom starred in several shorts back in the day. Most of these were good for their time. Other characters have followed suit and joined him in the animation department. Which is why we have so many cartoons today. I'll admit, I probably wouldn't watch cartoons at all if it weren't for superheroes.
Back to my point. superhero cartoons, by law, require a main character, or characters, that we find ourselves rooting for and attached to. Character development works for young heroes, but, for someone like Batman, you really have multiple ways of portraying his actions, either a silent caped crusader or a vigilante, who wastes no time getting the job done. Villains should not be overused, if a 65 episode show, most villains should appear in 2-9 episodes and their appearances should be spaced out, so they don't get stale. As I said earlier, few characters don't really need to develop as much as others.
A question I ask myself frequently is why don't superhero cartoons last long. Think about it, most superhero cartoons only last about 2-5 seasons. When was the last time you saw one with 6 seasons? Probably not in a while. This is mainly because companies, nowadays, put more episodes in a season, get tired with the show, and then, cancel it.
If Warner Brothers made a Superman cartoon, did six seasons of it, finished it and then made a Batman cartoon in the same continuity, with appearances by characters from the Superman series, I would be fine. Think about this, imagine a Green Lantern cartoon, five seasons long, cancelled and then a Flash cartoon, with occasional appearances by Green Lantern. Wouldn't that be a more believably continuity then the DCAU? You've got all these shows, with main DC characters, all showing up in each others shows.
If DC did something like that, I'd be in stitches. They could do one at a time, with 26 episodes each season and do a fan poll for what character they wanted to get the show treatment next. Doing this, would give so much more fans watching and supporting their series, they might actually start buying merchandise. I know a lot of people buy Justice League figures because they want a cartoon DC universe collection.