Why did this show take a nosedive?

It didn't take a nosedive, season 5 is great. I've enjoyed all seasons, some more than others but all are good.

There is only so much realism that someone can fake and make it
interesting and "real". I think the story just got out of hand, and
it spread, bled all over the place. With the weird sex stuff, and
Doug Stamper's weirdness ...when that goes on long enough that
you get a good clear look at it, it's silly.