To date I class Lost as being the best series I have ever watched, even hold it as higher than Stargate in that regard. I have watched it again since it ended and do enjoy watching it every time, but whenever I do re-watch it I end up missing it as much as I did when it first ended. It's probably one of the few series that's made me burst out in tears
Because of that I'm reluctant to rewatch as I have moved onto other shows and don't want to relive the sorrow (didn't really think that a television show could make me as emotionally attached but Lost managed it).
Here's a video which should better convey what I mean by that (Any fan should find it difficult to not miss the series after watching it). Recommend changing the quality of the video to 720p and watching it in full screen.