It... um... it was good. Although it had three things that made me kind of go 'argh'.
First, STUPID FLASHBACKS ARE STUPID. If you're going to give exposition by flashing back thousands of years, *maybe* you should make it interesting. Maybe there should be hints that more is going on than we already knew from season 1 episode 1. But no. Almost nothing else happened in most of the flashbacks; the Celestia/Luna one in particular was just utterly perfunctory.
If it's really a complete account, Luna was imprisoned for 1000 years for putting the moon up during the day for about 90 seconds, blowing up her own castle, and getting in a fight with Celestia. You know her original incompetent takeover that only lasted a few hours that everyone assumed was due to some sort of villain decay? No. No, that was her doing a much better job of taking over after planning for a thousand years.
Second, the Royal Guards were *literally down on their knees* begging Twilight to give them something useful to do, but she blows them off in two seconds and then runs off on her own to be stun-locked by low-level minions spamming status effects. You know what would have really helped there? A couple of Royal Guards!
Actually, no, wait, that was part I thought was kind of funny. The ARGH about that was Twilight being a complete dishrag. "Maybe you should go where it's safe?" "Um, okay." "Why are you back here where it's safe? Shouldn't you be helping your friends?" "Oh! Right. I forgot. Better run back to join them again. Alone. Through the dangerous forest. Without any guards or anything."
Oh, and she forgot how to teleport, although this is also not an 'argh'. She kept trying to use her wings and screwing up instead of relying on her magic which would have easily kept her safe, but that's kind of what people do when they get a new power.
So the third argh -- Zecora. Zecora pops out of nowhere with a random potion. Really? REALLY? Again? At least this time it was just magic drugs, so the annoyance of random zebra potion was mitigated by the whole cast staring at Twilight while she embarrasses herself tripping on hallucinogens.
And Applejack did a good job stepping up to the plate and being a leader... and a horrible, terrible job of actually making decisions. I'm pretty sure every single thing she did was wrong. Applejack, you are a silly pony. Don't give me that serious look.
"No, you're not missing anything. Your friend, Pinkie Pie." "That's meeeee!"
"Would I lie to you?" "YES!" "well, maybe?"
Also, I thought it was cute that the plants were a ridiculously delayed plan by Discord to free himself from the elements. It made his original defeat make a lot more sense -- he let Luna and Celestia blast him because he thought he'd be free in a day or two, but he underestimated the tree's power. Just like he assumed the elements were malfunctioning the second time when Twilight and company blasted him, but he underestimated their friendship.
...he really needs to stop showboating like that. Although I guess with the elements of harmony gone he doesn't really need to stop showboating like that anymore. *shrug*
So, yeah. Not my favorite episode, but it was fun to watch. I hope the other episodes are better!