The show was only 2 or 3 episodes in, and I'm a pretty impatient person, so I decided to look at the manga. The subject matter seemed interesting to me, so I figured it wouldn't hurt.
This series definitely falls victim to the original content being sacked/cut out for time. If I remember correctly, episode 12 ends around chapter 40? Each chapter is approximately 30-40 pages. That's a lot of content to cover for 12 episodes.
I hate to be that guy, but if you were/are hoping for stronger character development, read the manga. I binged all 59 available chapters that were currently out in about a week. I originally had the impression that Devil's Line was a Tokyo Ghoul copycat, but the story itself evolves into something completely different. It'd be a little rash to compare devils and ghouls, too.
This isn't a manga review, so I'll be talking about the anime from here on out.
The animation at times was weak and awkward. It was noticeably choppy more than once. The coloring of the characters and the background didn't mesh sometimes either. It looked like you were looking at two different scenes at once.
The ending really upset me. I won't mention what actually happened in the manga, but even if you didn't read the original content; the ending was horseshit. It was terribly rushed and wasn't believable in the slightest. Given how timid and stubborn Anzai is, he would not have reacted the way he had, nor would he have easily let go how much he hates himself despite how persistent Tsukasa is.
This is my own personal opinion, but I really disliked Kikuhara's voice. Not how I envisioned this originally well written psychopath's voice.
Now for the positives, I did like the music/OST/opening. I thought the ending was kinda lame, but I didn't hate it. I'd include the characters here, but for me they just weren't fleshed out enough in the anime. Lee wasn't as good of a comic relief either. Ishimaru is also one of my favorite characters in the show/manga. He's written more as a complex guy as well as someone who I enjoy to see because of the fact I find him to be pretty well written. The anime made him seem one-dimensional and boring. I was really exited to see him, but I was only let down.
Honestly, 6 is a generous rating.
