My sister tried to get me to watch Lost. I watched the first season, but then missed an episode or two. And the thing is, nobody could explain to me what I had missed. At all. They'd try, but it was weird and vague and just didn't work out. If people who watch this show religiously can't tell me what I've missed in one episode, it's not really worth me investing the time in any longer.
X-Files really went downhill after Mulder left. I stopped watching it after that.
I'm sure I'll think of more later. My brain is tired this morning.