This is what I like from "Men of Action"! (the group who made Ben 10) They made a dark themed action-cartoon!
Plot: An accident happened, an explosion. The explosion also released a massive amount of nanites, a small machines that causes a person to mutate. The mutation is random, if they activated inside the person's body. And then it came into the atmosphere making the whole world covered in it and thus, infecting everyone. Rex Salazar, a 15 year old boy that is infected with nanites, doesn't know his past. Agent Six, from an agency called Providence, found him in the middle of an EVO fight. (EVO, that's how they called the mutants.) When Agent Six saw his abilities, he saw hope! because Rex can absorb nanites, plus, he retains his intelligence. He can control his nanites. Now, he belongs to the Providence, an agency that deals with nanite-related incidents. He tries to find his past with Agent Six and Dr. Holiday's help.
Characters: Each one has their back story, well dark stories, they have nice agendas and personalities. Unusual ones. Voice acting is excellent.
Action-Value: The action value also depends from the season. Season 1 is dark, contained deaths and some sad events, it's balanced actually.
Season 2 lost its darkness, the deaths are not that existent. More focused on the action
Season 3, when the Black Night came, it became dark again. Such as in order to defeat the Consortium, a creation of the Black Night, he must lost his memory.
Art: A little differences from their art in Ben 10, really good. Animation is just like before.
Overall: 10. It's my preference for action-cartoons. Dark themed.