Well, though already mentioned during some conventions, they finally used the term "Alicorn"
They really showed Twilight's development. If it was before, she would have broken completely after she lost, but now she could keep calm and try to find a solution. Nice to see Zecora playing an important role in the episode.
When Zecora mentioned six, I thought they would use the elements, but the way the episode played out was much better. Twilight's magic tricks got me there for second.
I would like to know more about the Alicorn amulet and how Trixie knew about it, but again, 22 minutes weren't enough. There really are many powerful artifacts lying around Equestria (mirror pool, and now Alicorn amulet), so it would be neat if they get explained in some form, like the coming guidebook, though I doubt it. Also, now we know at least Pinkie's father is still alive, and his rock farm is still there. Neat detail.
I guess redemption would be the only option fitting of "Friendship is Magic" for Trixie. Hopefully we can see her again.
She already started working on it before the episode based on the episode previews.