Warning: spoilers in my comment.
There are a lot of shows and movies and such with supernatural elements these days. A lot. It dominates the market, and I get it - people like it. I like it too... sometimes.
There are also a lot of crime shows. Again, a lot. Most are not that interesting to me - often, it's because the characters aren't very good (in my favorite crime stories, the characters and the way they carry out the investigation are way more interesting than the crime itself).
Here's a show that got the modern drama aspect perfect - though it's all standard stuff really (though perhaps it seems that way mainly because it's more novel-like than most TV and movies), the characters and the setting (a character in itself) were outstanding and the story and the side stories were all intriguing and never dull.
It didn't need supernatural elements to make it good. In fact I would have been extremely disappointed. It just wouldn't have been right here.
This is actually exemplified by a point brought up in the review here, the perhaps-hard-to-believe way they made the break with the green-painted house. That did strike me as hard to believe, but not impossible by any stretch, and probably far more common and realistic than we think. Other crime stories have trained us to believe that breakthroughs come in more poetic and/or straightforward ways, or through sudden revelations (which this wasn't). I think we probably all know it isn't like that in reality.
Here they took the "making a sudden revelation" trope and played it out like it would in reality. It was a hunch and one hell of a long shot, and they showed the complete process of following up on it, finding the tax records, etc. - something that would normally be completely skipped over. And I mean, we know that this wasn't the first long-shot lead they followed up on - in addition to those shown earlier in the series, that's probably most of what they were doing in the office off-camera the last two episodes.
So in fact I quite liked that this is how they made the break that led to getting the guy. I'm sure there are other satisfying options they could have gone with, but everything I can think of as an example would have cheapened it, IMO.
I also think it would have cheapened it if one or both of them had died at the end. That would have been expected and too easy in terms of the narrative. This isn't a show about easy narrative and straightforward character development and so on. It worked great in a poetic way for Breaking Bad, though also not a show with easy narrative and straightforward character development, but would have felt off here.
I was in fact left a little underwhelmed by the conclusion, but not disappointed. Upon reflection (such as earlier in my comment), I don't think it could have ended any other way and still work very well. I like that the ending was very novel-like, and not a novel that offers easy answers and a straightforward moral at the end, but one that taps into something deeper and makes you realize that maybe there isn't an answer.
And I did like the small shard of optimism at the end from Rust, and given that this has already utterly consumed 17 years of his life, I'd like to think he's not going to stop the investigation into the others who are/were involved.