So, I got some of the references to Chambers' King in Yellow, parts of which I've read; others I looked up synopses of while watching the show. They seem to be not much beyond references: I was initially wondering if there would be connection to that world in the world of True Detective, like The Yellow King being a real play within the show, driving people mad, etc. But instead it just seems like the writers used the names Carcosa, and Yellow King as just simply references to the work, presumably they are fans of it. I thought for a while that instead it was these cultists who took the real-world Yellow King collection as literal or spiritual but we gained little insight into the cult. They rape and sacrifice children while in costume, and are... covering up a deeply disturbed, abused murderer? Like, I get it, he's in the cult, so you gotta cover up his stuff too, but it's seemingly like he's special in the cult, since everyone-knows-but-no-one's-talking, instead of offering him up as an expendable end, like Reggie "You're in Carcosa now!" Ledoux.
So, then there's the cosmic horror aspect: he's not a psychopath, or not just a psychopath, and he actually is 'ascending' or connecting in some way with some other plane of existence or alien dimension. Bierce's Inhabitant of Carcosa suggests Carcosa is not on Earth (it having two suns), so, alright. This adds a nice level of confusion in episode eight, where Cohle, alone in the temple grounds with Childress, is hearing the voice of Childress, and then has either a hallucination (we are reminded earlier in the episode he has had hallucinations) or a real vision of some strange galaxy-looking thing. The galaxy where Carcosa is? I don't mind this interpretation, it's interesting and ambiguous, which leaves room for the mind to wander.
But, philosophically, I feel like it was just a disaster! I was so disappointed. Throughout the series we are treated to references from Camus, Sartre, the Bible of course, I'm pretty sure some Dostoevsky (but I tend to see him everywhere!), and doubtlessly others who I missed. This nihilism vs existentialism vs faith (represented primarily in the Judeo-Christian form) was a fantastic dynamic. Cohle's nihilism is originally justified/rationalised away from himself, as he doesn't have the 'constitution for suicide,' and later embraced by him in his spiral away from society and his obligations -his missing years in alcoholism and endless chain-smoking. Philosophically unrested, though, he returns to finish the case. The question posed early in the series is more than, "How do you create meaning in life if there is no meaning to life?" but, "What is the meaning in solving the murder of one person if it destroys the lives of others, in a world where life is meaningless?" That is, the dead person is dead, there's no meaning left for her; but Cohle returns to pay a 'debt,' essentially abandoning his nihilism for existentialism.
Marty is very 'real' in his flaws and confidence, but fragility and need for conviction - even if they are convictions of convenience. But Cohle never has faith, not until his moment where he describes swimming into the depth where the love of his father and daughter united around him before he was awakened in the world that was previously meaningless.
There was no resolution to this conundrum - Cohle just suddenly feels optimistic. But wait, he is now back into the world that child-raping-cultist-murderers aren't always caught (the admission that they 'won't get them all' is met with a pretty mild sigh) and monstrous men very nearly butcher his friend. And he has, in his mind, a deep certainty of the real love of his lost daughter and father, beyond this world, so why is he optimistic? He briefly cries at being torn from it, and then is all, "Looks to me like the light's winning."
His evolution from destructive nihilism to resigned existentialism was perfect. Why did they steal that from, well, themselves? They could have simply left him in this new, less tortured place, or, frankly, let him die at the fulfilment of his 'meaning.' Perhaps the latter would have been too neat/obvious. Nonetheless the meaningfulness of the series seems to have, ironically, been emptied.
And this, just in case I've been too subtle, frustrates me a little tiny bit.