Over at Ta-Nehisi’s, I make the case. An excerpt here:
State of Play, and Prime Suspect, the British detective show for which Helen Mirren was justly famous before her revival over in the States, both use six episodes to solve single crimes. State of Play was a one-off, while Prime Suspect ran for seven series, in 1991, 1992, 1993, 1995, 1996-1997, 2003 and 2006. The size of the arcs let the main characters in both solve the crimes at stake while creating plenty of room around the investigations for character development not prompted by the immediate case at hand (something I think has always been a flaw of the Law & Order franchise: of course Fin meets his son on the job. Where else would he have time?). The shows felt more like watching the real lives of the people involved in the events in question, and the crimes feel like actual, extended, frustrating investigations.
The discussion in comments is well worth checking out, as it always is over there.