I've seen a lot of people saying that online. I personally think he was more of a plot device than a traditional villain. The story seemed to be more about developing Twilight's character than an adventure to defeat a villain. In that way he was more like Nightmare Moon than Discord or Chrysalis, I think. If they had more than 42 minutes he could have been developed, but as it stands I think Twi's development was more important than his. (Though I could appreciate some basic explanation of motivation at least.)
That said, Lord of the Rings managed 3 epic movies/books with a villain that's a giant holographic eyeball.
I watched it again, and it was a lot better the second time. A few things I noticed:
- Applejack is best pony, and I'm happy that she was much more than a background pony in this one.
- I liked the Twilight-Spike relationship. Such a cute brother-sister sort of pair, they.
- We heard the songs before, but I enjoyed the reprise at the end.
- Twilight's sonic rageboom and Pinkie's Fluttershy costume were huge laughs for me.