And I found out that it's really good. Better than many 'more adult' shows that I've enjoyed.
They have consistent characters.They have plots that aren't always wrapped up in a single episode. They have protagonists who aren't always right, and when they're wrong, they're wrong in ways that make sense for that character. They have an interesting world that works on different rules from our own, but remains internally consistent. They have characters who see their own world as the norm instead of seeming transplanted from our world.
And with all that, they also have a strongly positive moral message.
Most TV shows, whether for kids or adults, have certain kinds of problems always being solved by violence. Kids' shows usually involve beating bad guys up, adult shows often involve killing said bad guys. Violence is also the solution to a good guy turning bad - you beat them up and restrain them, then fix whatever is wrong with them against their will.
My least favorite My Little Ponies episode(s), the two-parter Return of Harmony, is what made me realize this most clearly. That episode, unlike the rest of the series, does solve the problems with violence. The contrast made me appreciate the other episodes even more - even the first season's two-parter, with its own big bad, is resolved peacefully.
Resolving conflicts peacefully is not only a good moral example, it also requires more creativity. A violent solution is always basically the same, while every peaceful solution is unique. In the superhero and crime-fighting shows I usually watch, very often I know exactly how the story will end - the hero will beat up the bad guy. In My Little Ponies, in constrast, I'm never quite sure how they will resolve the conflict.
And furthermore, in most TV shows, almost all conflicts result from villains. In contrast, most My Little Ponies episodes have conflicts arising from good characters who make mistakes. One episode involved TwilightSparkle, a diligent student, panicking because she doesn't have a lesson about friendship to write to her teacher this week. She is catastrophizing about how her teacher (the princess of the realm) will react to her being late with her letter, and running around town looking for a problem she can help a friend with. It gets to the point where she decides if she can't find a problem to solve, she'll make one. This is not a villain deciding to try to drive a wedge between friends in order to be evil. Instead, it's a good character getting herself into a mess and doing something bad because in her current mental state that's what makes the most sense. (The lesson for that episode isn't for TwilightSparkle, but for everyone else - even if a friend seems to be overreacting, you should take their concerns seriously because it's real to them.)