ZnT had an interesting concept, but it's not novel. It's basically a newer and far less thrilling version of Urasawa Naoki's "Monster" (which, by the way, is excellent). ZnT is about mysterious teenagers with 'evil' plans for the rest of the world and the super-smart, fallen-from-grace adult who is trying to catch them. It could have been an excellent story, but the anime is unfortunately so riddled with cliches and 'surprising twists' that it lacks any real suspense. ZnT also only has 11 episodes, which may not seem like a lot, but each season of "Free!" only had 13 and each still managed to have a solid plot independent of the other.
These characters are incredibly superficial. You are introduced to one facet of their personality and never get to see more than that. I could probably forgive that for Nine and Twelve, because they, as the main characters, are given more screen time, but absolutely not for Five, and Lisa, to a lesser extent. Five was a completely useless character. To me, she added absolutely nothing to the overall plot and only served to extend the series to 11 episodes - without her, this anime could easily have been like 6 episodes. I didn't see her final plot twist coming, and not in a good way - I was so disappointed with her exit because she could have been a good supplement to the existing characters, but instead, she appeared and disappeared and nothing about the story changed. At all. I also would have liked to see more from and about Lisa (personal favourite, because she's the most 'human' to me). Shibazaki was decent, but he was like a more cliched version of Tenma (from Monster). Also, I refuse to believe that the police are as incompetent/arrogant/stubborn as they are portrayed to be. Really, you're going to keep ignoring this genius detective, multiple times, even though he's clearly proven himself to be very intelligent about these things? Yeah, no.
Overall, ZnT is just very flat. There is nothing extraordinary about it; indeed, there are many, far superior manga and anime of the same genre. There are too many cliches, too many 'plot twists', too many dimensionless characters... That said, it's not awful. I think it could be the prototype, if you will, of a longer series that expands on the plot and characters, which could end up being interesting. So, if you're looking to kill a bit of time (each episode ~25 min) and don't particularly care about watching something amazing, then you'd probably enjoy this.
