People expect (or hope for) something great, because HBO has slapped the "True Detective" label on it, so they are disappointed when they get something average. This feels like a show I wouldn't have watched or maybe even heard about, if they had just called it something else.
So far, I think it's decent like you say - no more, no less. Episode 3 was a real slog, but the rest has been fine. I like the setting as well, but I don't really like how it is leaning into the supernatural. I can't really tell if it's supposed to be their minds playing tricks, because of the constant dark along with the mental illness of the sister character, or something actually supernatural.
Will be interesting to see how they wrap this up in just two episodes. Feels like there could easily be four or five left.