This is the video that got me interested:
I started wondering what all the hub-bub was about and before I knew it I was up to episode 4 and wanting more.
There's the nauseating amount of adorableness/cuteness of the characters. Then there's the great animation and visual aesthetics - it's awesome to see all the COLORS being used at 1080p, it's just NICE on the eyes after a week of gritty brown shooters k? The plot and humor is genuinely light-hearted but still funny to me as an adult.
It's sad that some people are only entertained by high-brow political jokes or jokes involving sex/mature shit, sometimes it's nice to get away from all that and laugh at the simple stuff I say!
Finally there's the creative community that has popped up around the franchise, about whom I could probably write an entire book about. Seriously, the musical and art talent has really sprouted from the darkest corners of the internet (as it always does when there's a uniting theme/topic!).
Hasbro + Lauren Faust have been accommodating with explosion of popularity, they chould've made the decision to reject the internet community because we're not all roses & tulips (there's enough gore/rule34 regarding MLP to make people's eyes bleed/brain impode and I'm sure Hasbro/Faust are fully aware of it).
Instead they embraced the community and keep throwing things into episodes, stuff that only the bronies will understand. E.g. Pinkie pulling the Gen3-face, to kids it would've meant nothing more than a quick laugh...but most bronies literally backed 5 meters away from the monitor yelling "HOLY FUCK...!!!!" while simultaneously exploding in laughter/awe at Hasbro & Faust for pulling that shit. I know I did. Seriously, nobody saw that one coming.
And that's why I love MLP:FiM.
For non-bronies...you don't have to watch the show with a critical eye, expecting it to blow you away because it has such a massive following. It's not perfect.
But you don't have to assume it's just for kids either, because there's more to it than that.
Remember, a sign of being a mature adult is the ability to enjoy EVERYTHING regardless of what age demographic it may (or may not) be aimed at. "It's for kids, I ain't even watching that" is something only said by those who are insecure about their maturity, or those looking to "act like adults" (but aren't) and don't quite grasp what it is to be an adult.