Let me explain my reasoning as someone who loves mystery; it's really quite a basic reason:
As a "mystery" and crime series, this falls hard.
The case-by-case episodes are so easy to figure out that it's an insult, and move way too quickly to get a decent grasp of the lore and other information which just sort of whizzes by.
By episode two, I think it's pretty freaking obvious that the protagonist has some relation to the dragons and-or at least isn't completely human due to what we've seen him do. Mostly, getting shot in the gut, cut on the leg, half blown up, tossed from a moving truck...he barely even reacts to injury. Not to mention being completely uninjured when we first meet him in episode 1 despite the carnage around him.
It seems rather silly that nothing about him has been revealed considering that by the end of episode 1 it was pretty obvious that he's not completely human.
Another obvious thing (to me) is that the guy who saved our protagonist in the first episode (and was 2's old partner...I can't remember the guy's name, or really any of the names except for Belle, but they have numbers in their names so I'm using that) is totally the guy with the scar on his face helping Nine.
I only have speculation on the "why" and "how", but it's way too obvious that's him.
Speaking of obvious, the anime's plot, and every event, is completely predictable. There's barely any tension (the most tension was when they had to disarm the bombs, and when that kid's life was on the line). In episode four, I knew who the criminal was and how they did it while said culprit was being interviewed by 7 and 2.
Now, I could be completely wrong about the protagonist and the guy with the scar...and if I am, then good on the creator of the anime for their red herring.