That episode was better than the last few but I'm just not buying Arthur as a compelling villain, He's a petulant child and that doesn't make for an interesting character.
I liked the whole Nimue as the original Dark One twist (despite it being predictable) but I still hate the fact that Emma's being controlled, it would be more interesting if she was in full control but she had lost her moral compass.
I'm glad that they're finally doing something with Zelena too, she's probably gonna end up being redeemed somewhat but I hope they make her more of a neutral character rather than an out and out good guy. I definitely think that Emma's gonna remain as the Dark One but she'll learn to control it, the conversation she had with Merlin was not very subtle and it reeked of foreshadowing.