Unfortunately, though, I don't have a whole lot of good things to say about it. The premise is interesting, to start. It is discovered that there is a type of not-quite human people walk the earth with us. People that cannot die. When they do, they simply get back up again after a few seconds. Not even Ajin know they are more than human until they die the first time. Little is known about them, so you have to learn along with the rest of the characters who they are and why they exist.
By far, the best thing about this anime is that it does a great job of addressing all of the question my inner critic comes up with. When I'm watching a movie, I'll say things like "That character wouldn't say something like that!" or "How did she know to be there?" and basically the entire time I was watching this anime, every time I said something like that, a character would immediately repeat my question, and it would either be answered or shrugged off when nobody knew the answer. (I'm more or less fine with the latter, as long as the writers acknowledged that I had a problem with it in the first place). So when a show puts a lot of effort into making it seem real, they did a good job. (One thing about that, though, is that in this universe the majority of the population seems to take a blind eye to somebody covered in blood. It happens more often than you may believe.)
Second, the world is also pretty realistic. What would happen if Ajin started popping up? The government would probably take the ones they knew about and use them as test subjects to see what was up. This is the main issue in the plot, so thumbs up again. All the side plots are pretty believable, too!
Third, the animation is a bit strange, as its done in full CGI. I wouldn't be surprised if people couldn't watch it for that reason alone, and I wouldn't blame them for it, either. You do get used to it, but I think traditional would still be all around better. The mummy ghosts are super awesome, though. The show is improved every time they show up because since they aren't supposed to look human they don't look out of place when they are animated using CGI.
And in general, the problems I had were with things that they could have done but didn't for no reason. The main character is somewhat sociopathic, I guess, as he has almost no feelings for other people (I realize that that isn't what it means to be a sociopath, but it is related). This, in my opinion, just makes me hate the main character for no reason. Disliking him doesn't drive the story, it just makes it less enjoyable because I kind of want him to lose. I like all of the side characters more than the main ones, and that is super frustrating! Also, a lot of the characters are needlessly ruthless, and while the show isn't particularly graphic, its unnecessary and takes me out of it because most of the general public probably would not be able to stab somebody in the arm with a tree branch, even if they did have a good reason. No, I'm not giving you context.
Lastly, and don't worry I won't spoil it, it has an unsatisfying ending. I have a really hard time suspending disbelief for how the "winning party" won, because it required a lot of variables that, realistically, would have been accounted for. The fact that it doesn't have a realistic ending is the biggest problem I have with the whole thing, because up until the last few episodes the realistic qualities the anime had were its best asset.
So, while the show is good, there are definitely way better ones out there. I'm also not a huge fan of really short animes, because I don't feel that its enough time to get invested in the characters. Also there's no time to establish plot twists.
I give it a Mummy Ghost out of ten.