Spoiler: S4 Power Ponies
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Well, I wasn't' disappointed but that is only because I was not expecting anything good to come out of this episode.

So the things I liked:
Villain was insane. Not Discord love-chaos insane but full on laughing-madly-wild-look-in-the-eyes insane.
Spike had a major role.

But other than that all there was, to me at least, was the similar garbage one would find in an action hero comic book. But, that is just my opinion. I never really liked those kinds of stories so I didn't really like this episode.