David Jason does the author's character, Jack Frost, justice, with his portrayal. He adds humor and pathos to him, thereby making him that much more of a realistic character and a better policeman overall.
That's what gives this show flavor overall -- just seeing that irrevelant humor every now and then, helps to make the show worth watching. The chemistry within the cast is good as well, they seem to get along well and they're all good actors. I look forward to seeing every new episode that comes out on dvd, due to all of that.
One of my favorite scenes was in either season nine or ten (pardon me if I got the season wrong -- it's been a while since I've seen them), when Jack got the promotion (even though he threw away the infamous "Grey Mullet" -- that was one of my favorite running gags from that show, it never failed to make me laugh) and as he was leaving the show, everyone saluted him. It was a class act all the way, and I loved how he kept the picture of himself in dress uniform, it showed how much he had grown as a character.
Hopefully the new season will come out soon enough on dvd, so I can again watch Frost and company go after the bad guys with class and style.