Shows that ended too soon but...

[QUOTE=Mean Mr. Mustard]

Barney Miller could have/should have kept going.

Same with The Dick Van Dyke Show
[/QUOTE]

Also, both shows voluntarily quit because they wanted to go out while they were still ahead.

I thoroughly enjoyed Reaper which was cancelled after two series. Great banter between the three regulars and Ray Wise as the Devil.

Early Edition Great premise. Reminds me a bit of Person of Interest without the insanely unrealistic gun play.

Picket Fences We needed to see more Fyvush Finkel.

Twin Peaks Of course.

Hmmm – the examples of “…ended too soon” that stand out in my mind don’t meet the OP’s criterion of “more than one season”. In both cases the shows definitive ended “too soon” because it was very clear that there was much more story to tell, not because it hadn’t creatively matured, or something.

Coronet Blue was a 1960s thriller series about a guy who is evidently in the espionage business and has lost his memory. He can’t find out who he is – none of his ID information is corroborated. The show ended before the Big Reveal that solved this mystery.

Alien Nation ended on a cliffhanger that was supposed to be resolved with the first show of the next season. The resolution was covered in a comic book, and the show continued on in a number of “specials” for years afterwards.
I suppose you could include “Firefly”, as well, for that matter – it got its own movie. But it was only one season. Like Coronet Blue, the network bounced it all over the programming slot chart, so it was hard to catch an audience.

Life. I’m convinced that I was the only one not related to the cast who watched this show, and that Jay Leno only came back to screw Conan O’Brien and my Wednesday nights.

I’m not related to any of the cast, but my wife and I watched it and liked it. I like just about anything Damian Lewis is in.

I really enjoyed that show, as well!

Dollhouse, Tru Calling, and Person of Interest all still had a lot of potential when they were cancelled. (But at least 2 out of 3 were brought to a decent, if rushed, conclusion.)

I came in to mention:

Stargate Universe
Community

And although they’re still on air but whenever The Simpsons and Big Bang Theory gets cancelled it’ll be too soon.

Grand. I’ve always loved Bonnie Hunt.

If Early Edition had kept going, I wonder how they would have handled the “why didn’t you prevent 9/11” thing?

(I’ve wondered the same thing about Seven Days, which maybe should be on the list.)

Of course I wanted them to run longer. That’s what the OP asked for examples of.

There was nothing in the OP that suggested our responses should be shows that have run between 2 and 5 seasons.
mmm