Honestly, I really enjoyed this episode. I believe that TV in general tries too hard to make episodes action-packed to capture an audience when it's not necessary all the time. Sometimes an audience really just wants character development and this episode having a slower pace and being more character reflective was great to experience, as well as being perfect time to do so considering Stiles being missing. It was a great way to make it feel like Stiles was part of the story without him being there, by having other characters immediately notice his presence being gone despite him being erased.
I really enjoyed seeing what Stiles meant to everyone in different ways and how they knew somebody was missing. The very foundation of Scott's life changes without Stiles, going all the way back to the night he was turned into a werewolf. Both he and Lydia were drawn to Stiles's locker during the episode, Lydia because she knew she was supposed to meet him there and Scott felt something when he passed it. It's interesting to see that Malia's already losing control of herself and her coyote side without her human anchor around any more. She's lost the memories of control she learned while she was with Stiles, which is very interesting considering as early as a season ago Malia still struggled to turn into her coyote form easily, but in the season premiere they made a point of it being easy and a regular occurrence for her now. I thought it might take longer for the pack to really notice something was missing, but it was really an immediate effect.
I loved seeing how Lydia's powers were manifesting in this episode. It made me emotional to see her reliving the night Stiles disappeared, down to being able to hear his words and feels his hands in hers as they ran away from the Wild Hunt. I assume the woman she saw sitting in Stiles's seat in class is something else that's been erased, as Lydia is getting clues about the taken ones, just like hearing a train in her bedroom and the promos having shown the erased in a train station. I also loved the callback to 3a with the automatic writing she did at the end of the episode, and how ironic it is that Stiles is the one who tried to get her to do it in season 3, and now she's doing it because of Stiles and actually writing his name (even if they don't realise it's his name yet).
I actually enjoyed the 2.0 generation in this episode, because their plot moved the story along. While I'm not the biggest fan of Corey's character, I appreciate that his abilities are going to be important in remembering and potentially getting back the taken ones. And I like that things aren't all happy between them after last season, Liam not trusting Corey and learning to trust him is probably a good start to him being ready to take over the alpha role from Scott when he leaves. Although I don't necessarily need this plot to be present in every episode, I don't care enough about Liam to spend time week after week building him up to be an alpha, actions speak louder than words, he needs to prove himself.
Briefly, I need to talk about Lydia's 'I think I loved him.' finally confirming what we've all known for quite a while now. Two episodes and two love confessions, if only she'd been able to say it to him! I feel sorry for Lydia, you can tell she's completely freaked out that there's somebody out there she's in love with that she can't remember. As if feelings aren't confusing enough normally, she's in love with someone who's name she doesn't know, who's face she doesn't remember, and who's voice she only hears in memories. But I'm really enjoying this season and the development of their relationship. It's unlike anything I've ever seen before.
Now for the big plot twist of the episode: Claudia? I don't understand how she's back, but I don't believe she's really alive. It's impossible for her to be alive just because Stiles has been erased, she's an anomaly. Everyone has forgotten Stiles and the things he's done, but that doesn't mean they didn't happen. Case in point: Scott was still bitten and is still a werewolf despite the fact that Peter (if you've seen the promos) has also been erased, he just won't remember who bit him. So there's no logical reason for Claudia to be alive, and even the Sheriff's first response was 'My wife?' because she shouldn't be there. I can't wait for them to explain what this means and why she's there!