At first this anime didn't strike me as interesting, but when I actually sat down and watched it, it instantly became a personal favorite for me. The main character at the start of the anime is a bit hard to like at first, but in the second season it focuses on him being able to hold his own, instead of hiding behind everyone else. The progression at the start of the anime is a bit fast, but easy to understand. Also the manga to this anime, is a bit more detailed and just as enjoyable, so check that out.
I gave this anime a 10/10 for these reasons. The story kept me entertained throughout the entire anime. The soundtrack went well with the anime and the opening is one of my favorites, the opening in the second season sucked though. The art is really good, but I would say the story line is one of its strongest selling points. Most of the characters were interesting to learn about. If I had to compare this anime to another then it would probably be Parasyte. Both are similar anime styles and focus on a character turning into a supernatural being.
Some of the negatives of this anime. I think the anime didn't go into enough detail as much as the manga did and skipped out on some important points that the manga focused on. The only other thing would be the main character at the beginning of the series, but nothing else really bothered me about this anime.
Definitely an anime I highly recommend!!! Give it a shot at least through the first episode!