Well, I just finished watching the episode, so here is my general review of the entire "Return of Harmony" saga (WARNING: SEROUS SPOILERS ABOUND!!)
Needless to say, after the first part ended, I have very little idea of where they would go with it next. But they went with it pretty well.
Seeing the opposite personalities of the ponies was pretty entertaining to say the least, especially Cruel Fluttershy and Greedy Rarity. Seeing the interaction, with their constant negativity eventually breaking Twilight, causing her to lose her faith in her friends, thus losing her colour herself, was cool.
The biggest surprise for me was probably the interesting move on Celestia's part, of making Twilight understand by ending her back all her friendship reports. A very interesting little touch, and pretty well done.
The various chaotic things going on in the back were heaps of fun to watch. When I heard that Discord as essentially a god of chaos, I was kind of expecting a more malicious sort of chaos, rather than simple surrealsm. But hey, it's still a kid's show, so I guess it's kinda justified.
Once again Discord himself was fun to watch, seeing him revel in his own madness, and not ven flinching when they tried to use the Elemens against him. But at the end, he kind of stopped being so creepy and insane, and became a little too silly. And when they use another attack from the Elements, epic and visually stunning as it was, he just sort of stood there and took it, like he knew he was screwed. Bit of a shame, but no big deal. And at least they did go with imprisoning him again, rather than turning him good or something (I've seen that done before several times, and it ever works)
But was the episode perfect? Sadly no. Once again, the pacing issues from the previous episode snuck in. Near the beginning it was fine, but the climax just seemed a bit rushed. I have to agree with what some other bronies are saying, that they could have made this story an hour-and-a-half film instead of a 40-minute 2-parter, so they could do more without the time constraints. But I guess being a bit rushed is better that dragging out alot.
And personally, I think the final scene in the palace made up for it by giving us what we last expected: A freaking Star Wars reference! I'm not kidding. You got the hall of the palace filled with ponies, the mane cast walking down the aisle to Celestia, who congratulates and thanks them, commemorating another window to them, with Spike standing on the side, to victorious orchestral music, before curtain-wiping to the credits, where the usual ending theme was replaced with another orchestral piece! It's clever, and certainly a unique sort of reference, and... well, unexpected!
All in all, the pacing was a bit jarring at times, but overall a great start to the new series. I would say that the rest of the series is gonna be great or epic, but I honestly have no idea what to expect with the rest of the season. But I'm living in hope, and eagerly awaiting the next new episode!