Well, put it this way, when I read that after the next episode there will be about another month before the rest of the season, I whined out loud and complained in an IRC channel full of other fans about it :p
I have no idea what's appealing to me, really. I never REALLY grew out of my love of cartoons- I still watch Disney movies even though I'm 21 and I love Kingdom Hearts because of all the references (and other things). I enjoy Fairly Odd Parents for some reason. So I guess it's not much of a stretch for My Little Pony to enthrall me.
A lot of the humour is great for me. I love Pinkie Pie and Fluttershy. I never thought I'd like My Little Pony after all the adds I saw as a kid, but this version almost feels completely different. The animation is great, the voice acting is top-notch, although cheesy the plots can be entertaining. Mabye it's because of the sub-culture it's spawned. I -love- that fan names for characters are becoming canonical- there was a character called Ditzy Hooves, but after fans called her Derpy that became her name. Along with 'Doctor Whooves'. The writers love that adults are enjoying it as much as the adults love the show. There's an Equestria Girls parody done by the cast as a commercial, which is great (it directly references 'bronies' and shows that the creators are fully aware of the fanbase). Songs are generally good too, even if they get stuck in my damn head!
So yeah. Good characterisation, great humour, fun stories, good fan base (mostly) and the show's owners are fine with fans using images and video clips to make stuff- they understand the whole culture of Internet memes and allow it, which shows respect, as I see it.
Random video:
http://www.youtube.com/watch?v=ITr90v7UaNg I'm a big fan, but not quite as big as that guy :p