The quest to solve the case was what everything was built around. I would say it was pretty central to the whole deal.
The way it was brought to an abrupt closure with the green monster, green ears, green house revelation was ludicrous. Then they walk to the lady in an old home and she remembers the color she got the house painted, the cost and the man with scars on his face accurately, all some 20 years after a simple paint job to her house.
The pictures, the videotape etc. all were of Marie Fontenot - a girl, whose name they had stumbled upon accidentally. Why weren't there pictures of other victims in Billy Lee Tutle's safe? These guys kidnapped and killed 100's of women and children but why did they make a show of the two women 17 years apart? What was the significance?
I found the whole last 10 minutes where Rust finds God a bit OTT too. It seemed like an attempt to overcomplicate thing to hide away from real issues. In the end all we need is God, rest everyone will get their comeuppance through natural order.