Super late, but finally caught up on this.
Yeesh. What a stinker of a season.
Doug Stamper. Doug fucking Stamper. This entire storyline felt like a lesson in "how to not fill your season with padding". Watching his story unfold was a lesson in misery, and not in a good way. His recovery, his attempts to come back, his mourning over Rachel, his awkward exchanges with his family, his alcoholism, his redemption through family, blah blah blah. All of it felt so "IN CASE YOU DIDN'T REALIZE, THIS MAN IS SUFFERING".
Sorry, but I just don't care about Doug Stamper that much. He's a nice ancillary character but I don't want to spend half the season on him and his mourn-porn crap.
Oh, and after he actually recovers, through his time with his family and the realization that Rachel is alive? All that time attempting to make him an understandable and relatable character, fully-realized and sympathetic? Eh, who gives a fuck? Let's have him murder Rachel, for no reason whatsoever.
Frankly, that entire sequence was pretty disturbing. We watch Rachel, perfectly happy in her new life, no chance of being found or noticed by anyone...and Doug just ends that. Why? He wasn't even going to kill her at the end of Season 2. Why now? Why freak out like the world was ending when you "found out" she had been murdered, if you don't really care?
And that's just Doug, not even mentioning the other lackluster B and C plots. This reason could have been 6-8 episodes without all the filler that added little.