I recently started re-watching Lost on Netflix. When the series ended I was extremely disappointed, but I still think it was an amazing show despite that fact.
There are two things that I find incredible about watching the series for a second time: how much of it I had forgotten and how much of it I "missed" the first time around. My college roommate actually got me into the show after the first season had aired. She had video-taped the entire first season and monopolized our little 13-inch TV/VCR combo for about a month before the second season began, so I didn't have much of a choice in the matter. But then I fell in love with it and was hooked for the remaining five seasons so it worked out.
I remember around season five or six when I hit a point of frustration with the show and tried to quit it, but there is no quitting Lost. I got sucked back in and finished out the series. Now re-watching it, I think I'm about at that point again. Of course I'll see it through... it's a lot less frustrating now that I already know the ending.