Having recently completed watching all fifteen seasons and twenty years of A Touch of Frost, I can say that's quite a run for any series. To be frank, I didn’t form the same kind of bond with the central character as I did with Vera or Jimmy Perez in Shetland. The plots were what stood out to me most, although there were some episodes where I dozed off and skipped ahead without realizing it—maybe watching TV in my favorite chair wasn't the best idea! Certain things are reliably present in each installment; he’ll invariably lecture someone about unfairness toward those who are vulnerable or have been wronged, poke fun at his superior officer, and generally stay a step ahead of him (although Mullett manages to score points frequently enough to make it engaging). He also tends to be tough on his subordinates, who seem to rotate fairly often, meaning they don't stick around for long. Thankfully, George provides some consistency. I wouldn’t describe DI Frost as undergoing significant development throughout the series; he remains essentially unchanged. He consistently disregards regulations and throws himself into risky situations. Toward the show's conclusion, there’s a slight indication that he begins to recognize the importance of giving women some room in his life—they tended to have similar turnover rates as his assistants. And it’s easy to see why he might start appreciating them more; while he never dates women significantly younger than himself, they are always attractive, unlike his own appearance. Still, it's television after all, not a reflection of reality.

Source on TMDB