Mega spoilers
Story - 6
This is like the To Aru series, a good concept but terrible execution. The story follows Nana who is talentless in a world where they are a bunch of talented people who are regarded as the enemy of humanity or sum. They were all sent to an island to "train" their abilities but in reality, they were being separated from the world because they are dangerous IIRC; as an "ordinary" human, Nana's mission is to kill all the talented on the island.
As I said in the beginning, the concept of this series is something that would rival the concept of Death Note, but the execution is terrible; this is Death Note but if L, Near, and Mello were portrayed to be intelligent but lacked common sense. The main problem with this series is the contrast to what, IMO, made Death Note so good, the lies Light was capable of making up alongside his brilliant acting made it extremely hard for L to say he was 100% Kira, in this series Nana is similar to Light in terms of acting but when comparing their deception, she is sub-par and her arguments as to why she can't be the killer are portrayed to be far more solid than they actually are.
I'll give the story a score of 6 due to being above average with a good concept but the characters are what really sells it short, what makes it worse is that I recently came around to watching Death Note and I can't help but compare them, but even without doing so if you are someone of average problem-solving skills you will likely find yourself pausing the anime and thinking about what just happened and asking yourself "Huh? Why aren't they asking x?"
Art - 6
The art isn't anything special but it is pretty appealing when compared to the average anime, it is something that doesn't really stand out but you can look at it and go "This is nice." Besides that, there isn't really anything else I really wanna say about it.
Sound - 4
Similarly to the art, there isn't really anything I can say about the sound other than it is ok, nothing revolutionary that hypes you up, but also not bad that it makes you focus on it. I can't really remember anything about the sound which is both good and bad since it implies it isn't memorable in being bad or annoying nor is it memorable for being good. The reason I am giving it a 4 instead of a 6 is that I like the opening and the ending, it is not something I would normally consider part of the "sound" but eh.
Character - 2
These characters are abysmal which for some reason that word sounds like a good thing. The characters are the main problem with this show, they are extremely dumb, and even when they catch Nana red-handed with their ability, she escapes by killing them since the character's character/personality allows her to find a way to exploit it and kill them without anyone finding out, I am posting this as of episode 6 and I can guarantee she is going to strangle that yellow hair girl that is a necromancer, how do I know that? Well, it is implied with the emphasis on an iron chain under her bed and we are 6 episodes in unless there is some kind of war where the talented rebel against the one holding them on that island with Nana leading the charge and somehow redeems herself to the point everyone accepts her, it is unlikely that girl is going to survive. While that explanation of how she kills sounds good on paper, it is awful in practice as she has always somehow lied her way out of the situation while logic dictates otherwise.
let me show you an example as to why these characters don't have common sense. In episode one, Nana kills one of the characters, it is later deduced by the antagonist (If you consider Nana the protagonist) and the time traveler that Nana was the last one with the dude that was killed in the location he was killed around the same time yet she is still alive, according to Occam's razor, if there are two explanations to an assertion, the one that makes more sense and has the least amount of assumptions is more likely to be correct, therefore should be considered correct until there is something proving otherwise. The assertion/question is who killed the dude/how did he die, was he killed by Nana, or was he killed by an enemy of humanity and Nana somehow survived, logic would dictate that it is more likely that Nana is the killer rather than the former, but let's move on.
As a side note, the antagonist may not have known if not just the time traveler but I don't remember what happened exactly and I am not about to rewatch and find out.
The second instance of someone dying was the time traveler, the time traveler was mostly with Nana in attempts to find out who killed/what happened to the other dude. The time traveler later dies, it is quite suspicious that the two people who were with Nana the most were killed, but let's continue. The third instance of someone almost dying was the antagonist or the yellow hair girl, I don't remember which came first but I think it was the antagonist so imma go with him. After becoming friends with Nana, an entire shed exploded and she was the first one to appear on the scene at a moments notice which would imply she was extremely close to the explosion while also holding the cat which was supposed to be in the shed where the antagonist was inside when it exploded and the only reason he was in there was because of the cat. The antagonist survived because he is immortal seemingly having some kind of regeneration. This would make anyone believe Nana was trying to kill you, seeing as she was the last person who was around you and the only person who could've known that you have no sense of smell, this is even more evident with all the previous suspicion.
I was going to continue over every instance but this review is too long so I'll just attack the recent killing. After the dude who can take photographs of the future died, they held a funeral where the antagonist was going to do an autopsy but was stopped by the Necromancer who said they can find out how the dude died and who killed him. After hearing this, Nana was gung ho on not doing it because they should let him rest in peace and later putting on an extremely weak act in an attempt to argue that this dude's soul was in pain and only stated this after finding out the necromancer doesn't know anything about his soul. She could've made a variety of arguments as to why not to do the autopsy such as it being morally wrong and he isn't a doctor or something of that nature in attempts to discredit his verdict or discourage anyone from agreeing to go through with the autopsy.
The antagonist could have easily exposed her as to why she is so against it and refuted each of her arguments while his verdict would've been supported by the necromancer, but he doesn't even challenge her arguments and just lets it slide and there wasn't even a reason for them not to do the autopsy, the weak argument given as to why they should not use necromancy is because the dude's soul was hurting. All the antagonist had to ask is "What is more important? Finding out how the enemies of humanity are killing our friends which would, in turn, save our lives at the cost of a dead person's soul hurting or leaving it be without any knowledge on how our friend died which leaves all of us at risk of dying since we have no way on countering it."
I would like to continue explaining other things like how her ability is easily refutable by asking bizarre questions or just asking "What am I thinking" then thinking about something that no one could guess unless they had the ability to read minds, such as "The souls of water is black" that makes no sense but if you could read minds you would be capable of guessing it. But I digress.
Enjoyment - 4
I am tempted to drop this anime because it annoys me at times and the characters make no sense, I believe in those paragraphs I made it very apparent why I dislike the series.
Overall - 5
Because 6+6+4+4+4 = 24/5 = 4.8
This series can be summarized as Death Note but the Death Note is replaced by abilities, L lacks common sense, and Light is terrible at lying while everyone else is mentally challenged and also slightly f'ed up or just lack skepticism.