Personally I've had a great takeaway from the podcast, not because of the sordid subject that's at the heart of it, but rather the amount of time and care the creators have spent looking at not just the crime, but also at the system and people that surround it.
Pop crime fiction teaches us a lot of things that Serial has gone to pains to refute - that eyewitness testimony is at all reliable, that people can recall mundane details of their lives at will, that a clear sequence of events is even possible to reconstruct, that the wrongly accused believe passionately in their own innocence, so on and so forth.
Serial has taken the popular notion of interviewing persons of interest, constructing a timeline, and catching people in brazen lies, and turned them upside down to expose the much more complicated behavior of humans underneath, and the fallibility of everything that these detective shows are based around.
The picture that Serial paints is markedly different from that of your typical crime drama, and that is an important takeaway. I think characterizing it as simply a gaudy way to "indulge in graphic death and horror" is overly cynical. In any case it certainly doesn't belong in the same sentence as any of the other crime fiction that portrays police work simplistically.