Wow, I was wondering how long it would take St. Elsewhere to show up on one of these lists.
If I remember correctly (because this was about twenty years ago, after all) there was a little boy who had Autism on the show. I think he was the son and grandson of two of the doctors, or something. Well, it turned out that the whole series was in the little boy's mind. The "hospital" was actually a tiny building inside a snow globe, and the boy would sit and hold the snow globe for hours on end, apparently imagining everything that happened in the series. The last episode revealed that his grandad was like a construction worker or something, and not a doctor after all.
The Seinfeld finale didn't live up to expectation, but it wasn't horrible. However, Nothing comes close to the complete suckfest that was the Sopranos season finale. I'll never forgive David Chase for what he did to the many loyal Sopranos fans.
I used to love that show and caught re-runs all the time, but the finale really ruined the show for me The last season was kinda weird anyway with the family winning that Mega Jackpot, etc but the last ep was the biggest downer ever.
Gilmore Girls - I mean, okay, it wasn't exactly "bad" in all ways but it just didn't feel like an end to a series, more like the end of a season. I feel like they just didn't tie up loose ends well enough.