I quite enjoyed it. It was intriguing seeing a villain who wasn't some sort of calamitous demon or world-conquering threat, but rather a fairly ordinary sort that happens to have a powerful spell and a twisted ideology. The writing for Pinkie Pie, Fluttershy, and Applejack was, I think, very very good, especially since those three are characters that some of the showrunners haven't really known what to do with in the past.
I think what I'm most excited about, however, is less what was in the episode itself, and more what it was building up for later. Talking about the "great mage Meadowbrook" and her powerful magical artifacts certainly has me interested - first of all, how cool is it that there's a character actually called a "mage" in MLP? And honestly, I'm very glad that Starlight Glimmer managed to escape: during the confrontation I was praying that would be the exact outcome, since I didn't think they had enough time for a satisfying defeat otherwise. This way, we have an established recurring villain, something that we haven't really had previously, and it gives us a chance to perhaps see more of Glimmer's backstory in the future. She was a good antagonist based on what we presented, but I would really like more of an exploration of her character as time goes on: what made her believe in her "sameness" ideology, and what made her take such extreme measures?
What I'm most curious about, however, is probably the biggest question of her character: does she truly, sincerely believe in the philosophy she's preaching? Or is it just a way to grab power? I hope that it's the former, just because a fanatic radical who's so far over the edge that she can't even recognize her own hypocrisy interests me more than your standard power-mad, cynical liar. She seemed sincere when she was berating everyone and claiming to be acting in their best interest after the reveal of her mark, so I have high hopes, but we'll see.
In short, a very good premiere to what I hope will be a great season. Looking forward to what comes next!