While this episode sure had some cool stuff that you pointed out, Bearcata, (like Stiles' FU to the agent who I think is Scott's dad, to Lydia and Stiles first kiss, to the teasing of what seems to be a romance brewing between Alison and ISaac), I find mself groaning at the contrived bits. First how nobody can find that damn tree, especially with Peter and Derek getting memory removal like that. Then the whole thing with the new "darkness in your heart due to substitute sacrifice" for Scott, Alison and Stiles which just smells like an early excuse to have a character go evil in a future season.
Also, I wish they'd explore more on Lydia being a banshee. How'd it happen? And I know I'd like to know her abilities and weaknesses better. So far it's been immunity to werewolf bites so she won't become one, she was being controlled by a dead Peter, she has a penchant for finding dead bodies, and a supersonic scream that only wolves can hear. She's such a mix and match of stuff, I wish the show would give a clear direction to her already.