Sunburst made that episode.
He was interesting, considering how male characters within this show are usually bland. There was some character development within this episode as well, and I think if they bring Sunburst back and build upon what has already been established, he'll be able to grow a bit more.
Starlight? Her change of disposition felt a bit rushed. I was expecting her to be way less communicative with Twilight, but then again, I suppose I don't know how much time has passed between the last episode and this one.
One thing didn't make sense to me; How Rainbow Dash and Applejack refused to tell the ponies that the crystal heart had exploded, and then as soon as Shining stepped up to tell them, they accused the ponies of not listening, when to my knowledge the ponies were never informed of the crystal's demise before Shining had arrived. So it seemed to me that this was purposefully done in order to build tension.
Some characters felt a bit one-dimensional at times, too. But overall I think the episode was pretty good. Some things didn't add up in my opinion, but I enjoyed it.