I thought the show was great when it was on.
Just because the "explanation" in the finale itself was disappointing doesn't mean that the show was trash after the first season. So, I don't think Lost really fits what this thread is about.
What I think happened was that they had a "Sci Fi/Technology" plan in the second season about the Dharma Initiative using technology to change the future. Then in the 3rd season they realized that that plan didn't give them enough material to drag the show out too much longer, so they flailed around a little while with standalone stories until they came up with a new "Sci Fi/Fantasy" plan involving ancient spirits/Egyptian gods or whatever. So the show kind of lost its overall and direction, but the quality of the show itself was high and I was still entertained so I can't really be all that angry with them about it.
Here's an example I can come up with:
"
Your Honor" on Showtime.
That show had a GREAT pilot. Then week after week it just got more and more unbelievable. Some of that wasn't their fault because COVID hit then while they were filming it, but Breaking Bad was hit by a major writer's strike in its first season and came back better.
IF Your Honor ended up the season stronger, they could have actually had enough material to continue on for multiple seasons as a great show, but now nobody is out there clamoring for a second season.
OOOO...I just came up with another example that's going to be super controversial:
24
I thought the first half of the first season was great. By season 2 Jack's daughter was running away from a MOUNTAIN LION for multiple episodes for some reason
.
I know most people will not agree, but I don't think the show EVER recovered from that.