All that really comes to mind for me are 24 and Dexter and Sons of Anarchy. But still those weren't the sudden hairpin turn into dog shit right at the eleventh hour. Sons of Anarchy was a fairly gradual descent, and 24 / Dexter went to dog shit after season 5 and just rolled around in the poop for a few more years, by which point everybody knew they should expect poop. With Dexter, I hate watched it for three years, hating every second of it but still taking it just to ride the damn thing out. With 24, I almost bailed in season 6 but hung in until halfway through season 7 before I couldn't take it anymore. With Sons of Anarchy, I spent maybe three years frustratedly enjoying it less and less until, like Dexter, I was just watching to see how it ended. But with Game of Thrones, I was still kind of shocked at how horrible it had gotten, kind of amused and confused. It hadn't been dog shit for long enough to turn into an obligatory angry endurance test to reach the end. It had transitioned rather abruptly into dog shit, so the transition was still jarring and discombobulating when the series ended.