Ok. I watch a lot of television, and I could go into a deep analysis of MANY shows / episodes. Instead, I'll just post a few thoughts I have (I may post more in the future).
In my opinion, the first three seasons of M*A*S*H were not good. I mean, the entire show was amazing overall, but I just don't like the first three seasons (mostly because of the characters). From all the shows I watch regularly, this show has probably the greatest range of quality from start to finish. First three seasons? I pretty much never watch. Later seasons? Some of my favorite television episodes. The finale? Best finale I have ever seen.
Also, the series finale of Everybody Loves Raymond. That last episode, in my opinion, was a bad episode, a terrible season finale, and as a series finale...why. Sure, it is one of those finales where things do not really change and the show could have hypothetically kept on going, but I am bored every time I watch that episode, and nothing really happens if you think about it. Sure, there MIGHT be some danger in that hospital scene, but we do not REALLY know (and there probably was not any danger anyways). Then the rest of the episode is pretty much the other characters obsessing over that. Yeah, and not even in an interesting way. I know they considered ending the series with the finale of season eight, which in my opinion would have not necessarily been a better place to end the series, but the season eight finale would have been a MUCH better series finale than the actual one. It could have been made significantly better, but even in its actual state, it is better than the ending of season nine.
For some reason, I have tend to enjoy more recent shows overall, especially the earlier seasons of them. I do not know if it is some new ways of writing or working on more current shows, but most of my examples of bad television come from shows that are at least before the year 2000. Again, I said most.
I may think of more examples, but I do not know if I will post them here. Just to be clear, I love M*A*S*H and Everybody Loves Raymond, but not ALL of them.