Sherlock is a good example. The first season (series) is really good and than they pull a Chris Carter and get all obsessed with the mythology and a single narrative arc. Each case is inextricably linked to the Grand Plot in such a forced and ham-fisted way that the inevitable conclusion loses all meaning and power.
I still watch it because I like the characters, though, as disappointing as the plotting has become.
I still watch it because I like the characters, though, as disappointing as the plotting has become.