One of, if not THE most perfect season finale anyone could ask for. It has some of the best and most memorable moments in the show, and not only is it the most emotionally powerful episode of any TV show I've ever watched, it also has great suspense, resolutions to mysteries and a super intriguing ending which makes you instantly want to watch the next episode. I personally can't come up with anything even slightly bad about this episode.
Review of Through the Looking Glass: Part 1
