This special had so many great lines: I can't decide if I like "Ohhh, Clover the- yeah OK I get it." or Pinkie Pie's "Yeah yeah, we get it. *LIGHT 'EM UP LADIES!!*" I especially loved all the in-jokes with the songs, fast forwarding through Wallflower's song was especially meta.
I also liked the twist at the end, where we learn that Wallflower was causing others to forget her interactions, which make sense why she was barely remembered at the school.
Finally, seeing Sunset face her Celestia again was so satisfying, Tara Strong's voice work for Twilight had me in stitches, and more Trixie is always a treat.
The only thing I can genuinely say I wasn't too fond of was the "misdirect" with the villains. I mean, it could only be Trixie or Wallflower, and given how much Trixie was hamming it up in the second act, it had to be Wallflower. I can excuse this though since, again, I liked the sort-of twist as to why Wallflower was often forgotten, and since I'm not the primary demographic for the show.
I don't want to call it too early, since I've only seen the special once, but if we were to consider it as an Equestria Girls Movie, I liked it better than the first one, better than the second (even though it had the best villains, bar none), better than the fourth, and I'd probably put it juuuuuust under the third. Maybe equal, not sure yet.