I'd wager that this is the greatest season finale of all time (series finales not included). Whenever someone asks me for an example of a classic season closer, I give them "Through The Looking Glass". Not only did we get a game-changing twist and fun new catchphrase ("We have to go back, Kate!") but we got more action and adventure than a major motion picture. This was the only time I wanted to call Time Warner Cable to thank them for their service.
We said goodbye to a favorite character and the story progressed in some major ways. Under the skilled direction of Jack Bender, LOST was always a show that was fun to watch. "Through The Looking Glass" wasn't only fun, it was mind-blowing. Just writing about the episode caused my jaw to unhinge and sink to the floor.