Shimary

*spoilers are very slight, but i do discuss story as a whole*

I want to start with praise first, since most important part of detective with horror elements is a story and it is good. It has foreshadowing when its needed, solid structure and some good emotional beats. Good work from special effects and make up crew creates visual hooks from the start too and if you are a fan of gory-type of horror they do deliver till the end of the series.
Unfortunately, this is not as good if you look and detective side of the story and its execution. Unlike slashers or horrors with high-schoolers, some degree of common sense is expected from cops, even if they do not believe in ghost from the get go... but no, people responsible for the script more often than not choose stupid as a solution. It is not as evident at the start (like arresting Thup, but not removing his belt), but gets progressively worse, culminating in 12th episode. Sometimes main characters acting dumb is not a big deal, but not in this genre. At least i strongly believe so.
Other thing, that i found even more unforgivable - inconsistencies in magical side of things. Any magic, including ghosts and curses, need to follow its rules. Instead, we have Thup, who is in constant danger from all ghosts in the world, until it just stops, and Singha who is a proper ghost repellant, until this stops working too. And at first the killings have to follow strict rules and even slight interference can ruin it, forcing killer to start over... oh, wait, its also not like that. And its all ended this a proper deus ex machina spell. So very disappointing, so easily fixable.
Romance part, unfortunately, also lives much to be desired. Main couple starts awkward and forced and continues to be out of place. I do wonder if fans of Pooh and Pavel loved it, but for someone not invested in them, it was like watching inserts from some other show, once again it was stronger the closer we got to the end. Second couple fit in narrative much better, but with much less screen time or even focus.
Good story bits are still good, some parts are even great and it is entertaining enough. But bad parts ruin it pretty noticeably if you prefer logic in your entertainment.