Some young people were discussing this show recently, and they complained that they "didn't get" why it was on as long as it was. They didn't get it because it isn't for them--yet.
As most long-running shows, the series evolved over time. Two major themes that continued (at least for me) are the beauty and permanence of the Yorkshire countryside (which is displayed more it seems as the series progresses) and the impermanence of the characters and, thus, us.
LOTSW teaches that we should redeem the time. Do the jokes repeat? Sure. In between, the Big Questions get asked and examined and sometimes even answered--as they have since humans first looked to the heavens.
Case in point: In one of the later seasons, Clegg complains about a manager he had in a job as a youth and how, even after all these years, he still harbors resentment against the man. Truly asks him what happened to the manager. Clegg gets a faraway look in his eyes and says something like, "He had the indecency to die as a hero in the war." The trio stand and silently drink a toast to the guy.
Loyalty. Love. Commitment. Friends. Family. These run through the series, and they are why, the older I get, the more this show resonates with me--the more I "get it."