I don't generally think very much of television shows for many reasons. Although I can't correlate the two events, when Magnum went off air in 1988 I stopped watching network television and haven't watched it since. I was never a big TV fan so when Magnum went off air it was just the reason I needed to turn off the tube.
Magnum was a great show because it offered fine actors usually giving excellent performances, great production values, always great music, and almost always interesting, and, frequently very moving, story lines that were typically believable. Magnum was never a super hero just a regular guy trying to make some money and have fun doing it. I can't compare Magnum to anything more recent but it does compare favorable to the Rockford Files. I can't recall the names of the great episodes but the last few involving Magnum's Vietnamese girlfriend were very good.