3) So what makes the show good? "Cute ponies doing cute things" gets you part of the way, although admittedly the Yotsuba effect will only do so much, and it isn't really a distinguishing factor compared to the rest of the media universe. The hints at worldbuilding beneath what is explicitly shown help as well - as ridiculous as it sounds from this distance, talking about a kid's cartoon, there's enough going on to give things real verisimilitude. To present some examples: mentions forward and backward between episodes, details of the mythology in the pilot that could not have been accidental and imply stuff about the nature of the alicorn sisters, cultural practices that are used more globally than just "instigation for this week's lesson, never to be mentioned again". And as for the storytelling, when in the hands of a competent writer (see #1!) the characters play off each other in interesting ways and the moral threats and resolutions follow naturally from their actions.
It's harder to explain why I like Friendship is Magic than why I like, say, Homestuck, or Gunnerkrigg Court, or Erfworld. It's probably far from the best thing on TV right now (heck, there's 10-year-old stuff on the Hub that I like just as much), and the show has its flaws, both global and episode-local. But overall, it's still a good-quality show, with the kind of heart-warming aesthetic that you don't see a lot in more "grown-up" animation. That and the verisimilitude of the setting (which is a big draw for me personally - c.f. the other /co/-related shit I like) managed to get me interested. And so far, I'm still interested.