I don't know, mystery series with a recurring main character (detective and friends), you can read out of order without missing much about that specific mystery, but you sort of miss the development of the detective as a character.
In some ways, some are almost like soap operas. A lot of historical mysteries are at least.
OTOH, something like say, Chandler's Marlowe doesn't really matter much. I'm not sure they were really in a series, just books with the same main character. And then you have Ngaio Marsh's stuff. While her detective, Alleyn gets married and have kids, it's sort of in the background, mostly.