Murder, She Wrote might be a set of comfortable cozies designed for the BarcaLounger crowd, but count me in. It also is a classy murder mystery series which, over 12 seasons with usually 22 one-hour shows per season, maintained a high level of consistency and viewer loyalty.
I think there are three reasons for this. First, the mysteries are solid. The writers mostly play fair with the audience. There are clues to be had if we're alert (although sometimes the clue may be so insignificant that expecting it to be noticed is optimistic). The mysteries often involve relationships among people with whom we're given the time to get to know. There seldom are out-and-out rotters. It's not always possible to spot the villain early, and when justice is done, thanks to Jessica Fletcher (Angela Lansbury), the conclusion is satisfying.
Second, Murder, She Wrote was shrewd in using the "So that's what happened to him (or her)" ploy in most of the programs. It can be immensely satisfying to a target audience of a certain age to come across once well known actors you haven't seen in quite a while. Lansbury and her producers almost always had strong character parts written for former marque names who still commanded affection and fans. In the Season 1 set, for instance, you'll encounter, among others, Howard Duff, Virginia Mayo, Martin Landau, Dan O'Herlihy, June Allyson, Van Johnson, Dane Clark, Jose Ferrer, Milton Berle, Stewart Granger, Eddie Bracken and Samantha Egger. These aren't stunt roles. The actors carry their weight. Angela Lansbury has always been a supremely confident and successful actor. She seems to thrive in having strong actors to play off of.
Third, and most importantly, is Angela Lansbury. Over the years her appeal and her successes in movies, on Broadway and on television have been extraordinary. She seems able to play anything with complete aplomb. Did a dance hall girl ever have a more suspicious mind or do a more generous act than Em in The Harvey Girls? Did a housemaid ever seem more sluttish than Nancy in Gaslight? Did a grandmother ever seem...odder...than Grannie in The Company of Wolves? Did a mother ever seem more like an ice-cold demon from hell than Mrs. Iselin in The Manchurian Candidate? Years ago I saw her on Broadway in Sweeney Todd as the deranged Mrs. Lovett. Whenever she was on stage she simply dominated the audience. The role of Jessica Fletcher, mystery writer and resident of Cabot Cove, is one she could have played with her eyes shut. It's to her credit as an actor that she didn't. She turned Fletcher into an immensely likable character, smart, experienced, shrewd and, above all else, sympathetic. The fact that we like Jessica Fletcher is due to Lansbury and is the reason the series lasted for 12 seasons.