I also love the retcon arc. I definitely was a little confused by how sudden June getting retcon powers seemed the first time I read it, but even then I was fully on board with what they did with the story after that point. I definitely agree how good it is for Terezi's character arc. I also like how it sets up the conclusion to several of Homestuck's themes with June being unstuck from canon allowing the character's predestined path to be broken.