For many, The Constant is the best episode Lost ever produced in its six year long run, and it certainly is one of the best. For me, however, there are better episodes, mostly because this episode is focused mainly on one select group of characters, where other episodes were able to put the same amount of surprises and talent into an episode that focused on everybody. However, don't let my nitpicking detract from how great the episode is. With this episode, Lost shies away from flashforwards and flashbacks, instead combining the two in an odd pairing of Desmond's memories with the events going on inside the freighter and on the island.
Upon watching the episode for the first time, I didn't appreciate it for what it was. By the time I got to the end, I was a little confused, mostly because Lost had rarely dabbled in time travel up until this point, and the whole idea of Desmond's 1996 self being sent to the 2004 self and having to interact with 1996 Faraday while the 2004 Faraday gave him instructions sort of sent me reeling. However, a second viewing reveals all sorts of previously unseen easter eggs. This is the beginning of Lost's descent into science fiction, their segue-way into a new genre.
Desmond was superb in this episode, and the writing gave him a lot to work with. I've always been a fan of Desmond's flashbacks. His relationship with Penny has always been a way to counter-balance the constant flip-flopping between Kate and Jack and Sawyer. Desmond and Penny's inability to be with one another stregthens the power of the scenes and in this episode, we see the show use this idea to its full potential.
While I felt this episode (I mentioned this before) didn't add much to the overall plot of Lost, it did act as the best stand-alone episode of the entire series. At this point, we didn't know that the Oceanic Six would be jumping around in time, living in the 70's and helping contribute to some of the events that they heard about in the 21st century.. this was a complex yet highly entertaining episode filled with great acting and writing.
Watching Desmond grow more and more desperate to find his constant gave an urgency to the episode that made it even better, and the quick cuts from past to present day helped perfectly create an atmosphere of chaos and confusion. This was just an all-around great episode of Lost, and one that I still remember as a stand-out years later.