Katherine was very Elena-like before she vamped out, with her whole "Yay, love! I believe! 蝴蝶 are pretty!" thing happening here. I do appreciate that even then, she wasn't psyched about settling for a guy who would ditch her for bar fights.
We also saw some definite movement when it comes to the central 爱情 三角形, 三角 of the show. Most importantly, there was finally some clear acknowledgement that it is a triangle, in a powerful and heartbreaking scene between Stefan and Elena.