First off, I love the fact that Lost is very much influenced by and very quick to reference literature. ABC features the Lost book club which is full of great books that really encompass the feel of Lost and everything it brings to the table. I wish there was one for Battlestar Galactica but I digress.
Through the Looking Glass was by all means a game changer. Where season three slacked, the second half built up to some of the best material Lost has ever produced which culminated with Through the Looking Glass. Everything had built up to this epic and action packed finale which payed off in a bigger way than any of us could imagine and showcased the biggest Holy Shit moment of all time.
Desmond was a bad ass, Mikhail died a few times, Hurley saved the day, and Charlie died. You can always count on finales to showcase someone dying and unfortunately it called Charlie's number. Though I don't think it was completely necessary it was fitting and his sacrifice was not in vain. It brought all the emotion and finality that was needed for season three and then it just blew our god damn minds with making us think that a flash forward was a flash backward.
The fact that it ended with this realization left me sour. At first I saw it as a glimpse of the end of the series, which we now know it wasn't. But I hated to see Jack utterly destroyed and unrecognizable. Thankfully that wasn't the end. Though Jack sucks now more than ever.
Through the Looking Glass will forever be one of the greatest cliff hangers (though not the greatest) that Lost has ever seen. The show was never the same because of it and that's what I love. Change came, and change is real. And that is what is great about Lost. Things change.