Just briefly, because I've got to go to work shortly:
-If that's what they were going to do with him, I, uh, kind of wish they hadn't bothered bringing Lancelot back at all. Between him being basically someone else in Lancelot's body, and Gwen being enchanted, the whole thing just rang rather hollow. I feel terrible for Gwen and Arthur, but it was all a bit too much artificially manufactured angst for me. Would have been far more interesting if Gwen and Lancelot had been themselves and unable to stop themselves.
-Don't think I really buy Arthur's Ragey McRage Rage reaction to Gwen & Lance kissing; I would've expected quiet devastation first followed by shouting, rather than the violence.
-This, uh, does not bode well at all for the magic reveal, does it? Sigh.
-The scene between Arthur & Gwen after he kicked everyone else out kind of reminded me of the round table scene at the end of last series - powerful taken in isolation, but didn't quite work for me since it was supposed to be drawing on previous development that wasn't really there. This was pretty much the first time I could believe those two really love each other, which is good for that scene but rather poor timing overall. Even earlier in the episode, I thought the engagement was cute but was mainly lolling over how Arthur was all "She's a good counsellor! She'll be good for the kingdom! Yay! ...Come on Merlin, it be sweaty men with lances time now!" Bradley and Angel both sold their respective devastation in that scene, so good on them, but ultimately it felt like a page taken out of someone else's story rather than the one they've been acting out since series 2.
-Distressed Arthur still ~does things~ to me, though. Come here, you poor thing, let me cuddle you. ♥
-The more I think about it, the more I really, really hate that Gwen was enchanted. And that no one, including her, knows it. Because now she's going to carry this guilt and have to redeem herself for something that was actually in no way her fault. It's this big ~thing~ between her and Arthur now, except it isn't a real thing at all - they can't work through their issues because there aren't any, there's just Gwen having no idea why she did that. Which sucks. If they really wanted to have Gwen/Lancelot fall-out followed by Gwen/Arthur making up, I really wish it had been legitimate fall-out, the two of them having agency and using it to make a mistake, and then dealing with that mistake. I'd much rather have seen Gwen make a bad choice because she had a choice, and then own that, as opposed to what we got, which is her having to act out the part of the guilty bad guy when she was actually a victim. Argh.
-I really wish Gwen had said she still wanted to be Arthur's wife rather than his queen. One of the biggest problems I've had with Arthur/Gwen all along is that she's always seemed to be mainly into the idea of Arthur The Great King Who Will Change Things, rather than Arthur the regular human. (Meanwhile, Arthur seems to be into her mainly because she's a female version of Merlin in a lot of ways, but that's a different issue.) I don't think she's looking for power or prestige for herself, but it kind of feels like she still sees marrying him as taking her place by her king, rather than with her lover, which doesn't make me particularly root for them as a couple.
-Nobody finds it the least bit suspicious that Lancelot magically came back from the dead right before the wedding, macked on Gwen, and then topped himself? No one? Really? Not even with Gwen talking about how she didn't know why she did it, she was unstoppably ~drawn~ to him? This, in a kingdom where someone gets enchanted every other week? Not even Merlin thinks to question whether someone might've messed around with Gwen too?
-WTF, Elyan, your sister gets engaged to the king and then banished and you don't have a single thing to say to her on either subject?