I have watched the "Return of Harmony Part 1" episode a few times through now (I am ever more rapidly spiraling downwards into Bronydom, I know) and here are some of my own personal thoughts about it:
First of all, I've tried, but I can't help but shake the opinion that this storyline is too much of a rehash of the Season 1 opening story, "Friendship is Magic" parts 1 and 2. I know that I am not the only person here who has picked up on this. Even worse, I feel that the season 1 opening story involving taking down a villain with the Elements of Harmony was *much* better-- it setup the locations, characters, and mood for the series very well, etc. Unfortunately, the plot of the new episode "Return of Harmony - Part 1" really gives me the impression of "here we go again" far more than it makes me think that the series is going somewhere new and exciting that I haven't seen before. On top of that, the overall tone of this episode seems somewhat darker than any other episode that I think that I have seen for this series-- it doesn't really seem to quite fit with the overall bright and warm tone that all of season 1 had, and I have to wonder if some of the more creepy elements like the talking apple piles, the mocking balloon garden, and the creepier than usual music soundtrack might be a bit off-putting to the youngest viewers that this show is supposed to be targeted at. The original villain Nightmare Moon and her antics weren't really all that dark or imposing by comparison. I am not saying that MLP:FiM shouldn't have a more serious lot every now and then, but as I said before the more foreboding tone of this episode just doesn't seem to quite fit with the tone of the episodes from season 1.
Also, as of this moment anyway, I am not sure if I am really pleased with the new villain, Discord. I have nothing against the voice actor John de Lancie or his performance-- those were fine, and I did enjoy him back in the day when he played "Q" on ST:TNG. Instead, the two things that I don't like about Discord are his (lack) of motivations for being evil, and the fact that he seems to be all-powerful. To explain my first point, I absolutely hate villains that are evil just for the sake of it. I usually view the world as shades of gray instead of just in black-and-white, so I like my heroes to have a little bit of dark in them, my villains to have a little bit of light in them, and for the villains to actually have a reason for doing the evil that they do instead of just doing evil to be evil. For example, back when Princess Luna became Nightmare Moon, she wasn't originally evil, and her turn to darkness wasn't an overnight transformation. Instead, she slowly became more and more upset that the ponies of Equestria enjoyed and were grateful for the daytime that her sister brought, but slept through and were unappreciative of the nights that she brought. This resentment grew and turned to jealousy, and finally caused her to turn against her sister, who she focused her bitterness against. Add that to the fact that Nightmare Moon was imprisoned in the moon by her sister for a thousand years, and there is some real motivation there as to why she would want to seek revenge against her sister and wreck everything that her sister had built. And as horrible as that is, Nightmare Moon wasn't inherently evil-- she was just a pony that let her jealousy and bitterness consume her. That is a very human backstory, and you can relate to it. Who here hasn't felt spurned by someone who upstaged them at some point in their lives? I don't think that the same can be said for Discord. Sure, you can say that he is also resentful for being imprisoned for thousands of years and displayed as some kind of trophy in a garden, but that doesn't explain why he was originally evil and had to be imprisoned to begin with. I hope that they delve a little more into his backstory in part 2, because villains that are evil only for the sake of it are rather one-dimensional characters. As far as I'm concerned it's the villains that make the story, and I would like Discord to turn out to be an engaging one.
For my second point, as far as why I don't like Discord being seemingly all-powerful is because having a seemingly invincible foe often causes an unresolvable conflict for the heroes, and that can lead to the use of deus ex machina plot devices as a cheap way to resolve that conflict. For example, I don't want to see the situation against Discord look utterly hopeless for the ponies until all of a sudden there is an unexpected and convenient appearance of a brand new powerful event, character, ability, or object that somehow defeats Discord and saves the day-- that can be rather unimaginative. If your villains have human weaknesses and flaws on the other hand, you don't need to resort to deus ex machinas to resolve things-- you can resolve the stories through clever use of the characters' current talents and abilities to exploit their weaknesses rather than having some new unlikely invention, event, or ability resolve it for them. As a side note, I also hope that the writers don't go down the other overused route of having the ponies somehow trick Discord (possibly by having him unintentionally break the rules of one of his own games) and fool him into re-imprisoning himself or leaving or something. I would really like to see some kind of imaginative, unforeseen, and entertaining twist for the ponies to save the day here. Like Ziel speculated, it would be interesting to have the Cutie Mark Crusaders somehow play an instrumental role in resolving the conflict in some way, especially since they were the characters that kicked off the events of the plot by releasing Discord to begin with.
I was also kind of surprised by how easily Applejack submitted to Discord's ruse in the hedge maze. While I like the idea behind what Discord's message was (that it is sometimes easier to delude yourself than it is to accept a hard truth), Applejack succumbed to it with nary any resistance at all. Even Rarity showed greater resistance against Discord than Applejack did, and she didn't have an entire episode of the series solely dedicated to her steadfast dependability (e.g. Episode 4 - "Applebuck Season"). With Fluttershy I did enjoy Discord's forcibly turning her mean as it broke the pattern of the story and it was an unexpected, but at the same time it lowers my opinion of Discord because it shows a lack of patience and cunning on his part. He was the one that said he liked games to begin with, yet he was quick to cheat at his own game as soon as Fluttershy showed the slightest bit of resilience against him and his methods. Lastly, I felt that Discord's trick against Rainbow Dash was one of the best since having the ponies lose Discord's game through Rainbow Dash leaving the maze was not something that I saw coming. It really makes you wonder what is going to happen to the ponies now that Discord has won the "game," and how they are going to escape that situation.
Hopefully I don't sound overly negative about the season 2 opening episode. Overall, I felt that this episode of MLP:FiM was pretty close to MLP:FiM's usual high standard, and for all I know all of my minor misgivings may still be resolved in part 2 of this story-- it is really kind of hard to accurately critique anything when you've only seen half of the story! In any case, I will be looking forward to watching the resolution of this story on my DVR on Sunday night once I return home from the vintage computer fair that I am attending all weekend!