A show that seemed to have become popular over time and has been influencial was Kolchak: The Night Stalker. It's strange that it ended so soon because it was a damn great show and they had great ratings. I learned recently that they had a problems with star McGavin and also the shows were too expensive + other problems so they ended it.
The X-Files for a long time it was my favorite show but after their 1998 movie when they revealed pretty much the whole thing, the tv show never recovered and not too long after David Duchcovy decided to only stay as a part-time character and it was never the same since he was the soul of the X-Files. Casting two new leads was a mistake, having super-soldiers was ever worse. It went nowhere fast.