Best TV Show That Only Lasted One Season?

I totally agree about Freaks and Geeks.

In fact, I enjoyed that show so much that last year soon after the Covid lockdown hit, I bought the boxed set Blu-ray Collectors Edition of the show.
It was quite the package.
Included was the complete series (18 shows) in the original broadcast aspect ratio as well as the complete series in widescreen.
In addition, there were 28 commentaries from show creator Paul Feig and executive producer Judd Apatow, cast members, the crew, and even fans of the show; two hours of audition footage and deleted scenes from every episode; outtakes, bloopers and alternate takes from every episode; behind-the-scenes footage, plus a digital yearbook.

Another single season show that I also enjoyed was Square Pegs. That one lasted 20 episodes in 1982-83.
I refused to buy the DVD of that complete series however because unfortunately, due to budgetary constraints, they changed the music that was heard in many of the episodes. Apparently they didn't want to pay to put the music that was heard during the show's broadcast onto the DVD package, so they inserted different songs from other artists. Too bad, because the songs that were originally used were very good and made the show that more enjoyable. One of my favorite episodes was when Bill Murray guest starred as a substitute teacher. There was one scene where he danced to Billy Idol's Dancing With Myself. It was great. Sadly, that scene lost some of its punch in the DVD without that song.

I agree with Freaks and Geeks.

I will add My So Called Life. I loved it when it first came out and I totally related to Angela. I watched it a couple of years ago and I was totally relating to her mom.

Freaks And Geeks, definitely

The Adventures of Briscoe County Jr.

Firefly as well

"Invasion", a Sci-Fi series, was pretty spooky and good.

Besides agreeing with some of the ones already mention, I would add: "Studio 60".

The first half of the season was really good, I believe they produced the last couple of episodes already aware they had been cancelled and everyone just gave up.

Also, "Eerie, Indiana" and "Luck".

Freaks and Geeks was also my top choice. That's awful hard to top it.

I doubt if anyone will remember this one: Otherworld, which ran for only eight episodes in 1985.
https://moviechat.org/tt0088587/Otherworld

I liked it at the time... don't know how much I would like it today. It probably hasn't aged well. There were rumors that 13 episodes had been produced. If this is true, I wonder whatever happened to the five unaired programs.