S1, for me, set the tone by saying this was a show about three things:
1. Police who have been broken by their jobs, forced to reconcile how what's RIGHT isn't always what is LEGAL, and vice versa.
2. A strange and horrific murder case that seems to edge into the occult
3. A present tense frame story that looks back at a previous time as the case is re-examined.
As an anthology, I knew it was going to be a different case and cast each season, but it seemed like those were the core ideas everything would be built around. And that wasn't just my assumption, I have a copy of Pizzilato's pitch and it says future seasons would always be about a pair of investigators that are set against each other, but have to work together on a case that spans over a long time period.
So when the second season came out and was just a very by the numbers corrupt cop in LA storyline, I was disappointed. I wanted it to be rural, I wanted a hit of the occult. I wanted more of the things I liked. Aside the shoot out episode and the one where Rachel McAdams goes undercover at the sex party, the tension was flat as hell.
Season three seemed to return to the form of season one, but it was so boring I never finished it. And I watched it during lockdown when I had nothing to do BUT watch TV shows.
Season four is a return on all fronts, though I suppose the present-day investigation looking back only comes into play in the last episode. I don't think it was flat at all, I think each episode advanced the case in interesting ways, and the ending-- which still hints at something supernatural but also gives a logical conclusion, worked great.
I do think they left one too many thing unanswered for (the tongue) and it did feel rushed that both Annie as well as Danvers/Navarro could spend five minutes in the under-ice lab and instantly have all the answers, but beyond that, I was very happy and did not think the bed was shattededed.