I thought the finale wasn't bad, but it definitely didn't end the way I expected or would have preferred. I was led to believe by episodes like Frenemies that the villains would reform in the end, or at least admit they were friends with each other. I could see Chrysalis saying something like "Our friendship is better than pony friendship. Let's not let it corrupt us." What happened at the end felt more like a zap the bad guys cartoon cliche, and I've come to expect better from Pony. I feel that an opportunity to really drive home the show's core message for 9 seasons, friendship is magic, was missed.
Discord. I have a huge problem with his both suggesting the punishment and then executing it. He brought them there in the first place, they were no threat until he did so. And he gets a free pass? That really didn't sit well with me. His smugness at the end made it even more annoying.
I'm a Chrissy fan, so I would have liked to see her reform most. That would have made the episode a home run for me. Having said that, I know she was the architect of her own fate by being too stubborn for her own good, including in Frenemies. Continuing to run her mouth after the villains were clearly defeated probably didn't help any. At least she went down swinging, and made sure no one would ever forget her.
People throw around the words "forever" and "all eternity" in connection with the villains' petrification. I disagree, and Discord himself is the proof. If Twilight found a way to get them to buy into friendship and not be a threat, I think she would free them. I feel that even in her traditional friendship speech at the end, she was giving them one more chance to change ("those who find the light"). She is the Princess of Friendship, and she's also in charge. I just hope Chrissy and the others are in a state of suspended animation, even though Discord said he could hear while trapped in stone. I think thier minds or conciousnesses at least are intact, and it would be awful to be awake and aware and stuck like that. As to how long they'll be petrified, I'll just say forever...for now.
But with that said, I'm not sure what else they could have done with the villains. Clearly they had to get the book thrown at them, and Tartarus probably wouldn't be an option because what if they got out somehow. Chrissy's threat about them always coming back might have been an empty, defiant one but I can understand that Celestia and the others had to take it seriously. They had to stop them somehow. Someone said Discord might even have saved thier lives by suggesting petrification, because Celestia was probably ready to kill them after Chrissy's rant. Again, I wish things had worked out differently, but it is what it is.
So I wasn't completely satisfied with the finale, but Pony has batted 1.000 up until now. A .999 average to finish isn't bad.