After the best run of episodes on "Lost", "Through the Looking Glass" pretty much had to be absolutely phenomenal Series finale of any shows ever aired and also the Most Shocking Revelations Ever. A brilliant action/adventure epic balanced by a real care for and attention to the characters who remain the core of "Lost", "Through the Looking Glass" really feels like a top quality feature film, much like all of the other finales.
Almost all of the core characters are given a key role here, some of the dialogue, both dramatic and comedic, is absolutely excellent (although there are one or two bad lines as well), and the Jack-as-Moses stuff really does work. Charlie and Desmond get some of the meatiest stuff in the episode, and Charlie's death scene is really very well-done. Now that I've seen this episode at least five times, however, I can safely say that I don't like it as much as "Live Together, Die Alone", which was simply a superior achievement in almost every way, and fell short of this only in that it didn't have a massive game-changing shock ending which took everyone by surprised. That's not intended as a criticism of "Through the Looking Glass", but merely further praise for the simply phenomenal "Live Together, Die Alone". Also, "Through the Looking Glass" had a much better follow-up than "Live Together, Die Alone", but really in comparing the two episodes much more appeals to me in "Live Together, Die Alone".
"Through the Looking Glass" boasts perfect performances from basically the entire cast, I think that Matthew Fox gives his best performance here. A lot of people say that the flashforwards aren't interesting on their own, that they only become interesting when you find out that they're flashforwards. This might be true of the first viewing (though even then they are more enigmatic and mysterious than any other Jack-based off-island stories), but on repeat viewings I find them absolutely fascinating and iconic, though, I admit, not as great as Desmond's flashbacks in "Live Together, Die Alone". Matthew Fox's performance is a big part of my enjoyment of the flashforwards, but the coffin mystery, the dark, dark moment where Jack nearly jumps off the bridge, the one shot looking down at Jack and the coffin, and the final scene with Kate are all very memorable aspects of the episode.
On the island the story is very action/adventure based and works very well on those terms, with both the action scenes here being among the better ones on the show. Jack Bender does a great job of directing the episode and by the time you've gotten to the ending, which, let's face it, is what most people talk about in relation to the episode, you've already enjoyed some of the finest populist entertainment around, and with some amount of intelligence as well.