The Constant

I'm flying through season 4 of Lost, but i've slowed down in the wake of the episode called THE CONSTANT. This episode introduces us to time travel on Lost, and the implications of it, for the first time since Desmond learned about fate.
In terms of setting the scene for time travel in season 4 and 5 this episode is perfect. We receive a foundation that gives us insights on Daniel and lets us in on the island's secrets.
More importantly, though, we're given a great love story. The roller coaster of emotions we go on with Penny and Desmond throughout the episode is one of the greatest rides I've ever been. It comes to a climax with a phone scene that by the end has me in tears with Penny.
This aspect of Lost is why I am in awe of it. Not only am I caught up in the mythology of the show, but I love individual episodes. When the writers want to they can knock an episode out of the park in this way, and for that I will always worship at the alter of LOST.