Shows that never should have went beyond the first season?

Orphan Black (2013-17)

The first season was great and the next four seasons were increasingly awful.

The Leftovers (2014)

It had a great first season and then just ran out of steam.

Soap (1977-1981)

The first season was brilliant & groundbreaking.

Although S02 was quite good as well, the cracks were beginning to show. S03 had it moments, but it really was starting to wear thin. S04, the final season was a total disaster.

Prison break.
It should have ended with Michael and His brother finally escaping and that’s it

Batman burned incredibly brightly for a short while. But it went downhill pretty fast, too. Opening Season 2 with Art Carney as The Archer pretty much says it all. There were some bright spots after Season 1, but overall...meh. Still, without Seasons 2 or 3 I don't know if it would be the iconic thing it is today.

According to what my dad and brother said, "Westworld" should be among that number, because all the seasons after Season 1 stank worse than a dead whale.

Heroes (2006 - 2010)
Loved the first season. Then it just....fizzled

Twin Peaks (1990-1991)
I know it only had 2 seasons, but I think it could have been even better if it had just been a limited series with the mystery of who killed Laura Palmer

Maybe Misfits (2009). Season 2 was okay, but it could've easily ended at season 1.