I was shocked at the conclusion of Season 1... absolutely stunning conclusion to a great season. I don't recall being that invested in a drama series since a couple of lifetimes ago; maybe because lack of writing in todays dramas, I don't know, but after making the leap of a couple of lost characters, the theme of AC12 and its role as the center-piece became clear. Hastings, head of AC12 who started out as the irritant became the backbone of the series; finely done.
The writing, from the Line of Duty perspective of the police investigating "their own", at first reminded me of a dog chasing its tail, and since that first season I've come to have high regard for this type of police procedural. Everything about this series is first class. I'm no professional but I'm impressed.
Season 2 and 3 are remarkable, again, for its production and acting. I think it holds up much better than the Wire did, and without being too closely comparable with True Detective story series, which was amazing, this is top shelf.