Season 4 - Favorites
[4.05] The Constant
[4.13] There's No Place Like Home (Part 2)
[4.14] There's No Place Like Home (Part 3)
Season 4 - Honorable Mentions
[4.03] The Economist
[4.07] Ji Yeon
[4.12] There's No Place Like Home (Part 1)
"The Constant" is generally regarded as one of the best episodes of the series. Instead of us seeing a flashback of Desmond's character, we actually follow his character as he bounces back & forth in time. This serves as more proof that Desmond is special when it comes to properties of space, time, and consciousness. And, it gives us one of the series' most emotional moments as Desmond reunites with his love Penny albeit over the phone. Hearing Penny's voice helps ground Desmond such that he gets his memory back in the present and stops bouncing around in time.
The three-part / four-hour season finale is one of the most exciting story arcs of the whole series. We see events that eventually lead to some of the characters getting off the island, though not in as easy a way as we might have expected. I can't remember exactly why, but I count Part 1 as an honorable mention instead of a favorite probably because the action and intrigue was just ramping up at that point.
"The Economist" is definitely the best Sayid story. In retrospect, it's a little depressing though. When combined with what happens to Sayid in season six's sideways universe, it's pretty obvious that Sayid was perpetually screwed. No matter how hard he tried to redeem himself, on the island, in 1977, off the island, or in the sidewaysverse, he was always meant to be a killer. It reminds me of a line from the otherwise forgettable 1996 Michael Douglas film "The Ghost and the Darkness" in which his character, a famous hunter named Charles Remington, is hired to kill two lions reeking havoc on a railroad operation in Kenya. Someone asks Remington if he enjoys killing and if not, why do it. Remington responds, "Because I've got a gift." It's the same with Sayid. His gift, but also his curse, is his ability to torture and kill.
No surprise, but "Ji Yeon" is another honorable mention simply because it's a Sun-centric episode. I love the part at the end when Hurley goes to visit Sun in Seoul. She and Hurley take Ji Yeon to a grave that is reserved for Jin. At that time, we still didn't know if Jin was really dead, on the island but pretending to be dead to the outside world, or assumed to be dead by the Oceanic 6 but actually alive. Consequently, another tear-filled moment.