It's rather amusing with lots of self-aware and under-the-radar humour (Lauren says she was aiming for the Pixar effect by appealing to older fans), and some funny implications (in one episode Applejack gets tired over-working, but the way she acts as a result makes it seem like she's stoned).
The characters are incredibly cute (especially Applebloom and Fluttershy) and really expressive, plus it's got songs which have a tendancy to ear worm.
And on /co/ it's approaching Team Fortress 2 levels of memetic mutation:
(Also I got 10 out of 12 on that quiz, god help me)