A good series overall, and mostly that it made me like a character I used to hate.
In researching more about Yandere to satisfy my own macabre curiosity, I stumbled upon Gasai Yuno and found Mirai Nikki.
The premise was interesting enough, a socially-inept boy given a prescient diary and thrown into a fight to the death for godlike powers and his yandere stalker. But after a while, I started to root for Yuki (poor incapable, bewildered kid caught in dangerous circumstances) and dislike Yuno, because after the novelty of her cute-and-murderous-with-no-qualms persona, being a typical Yandere, I could not find any other redeeming qualities in her. She was an unstoppable force and flat character, and seriously starting to annoy me. She killed of my favourite character, which was Akise Aru, and that act was the one that began my hatred. A girl solely dedicated to one guy with no personality other than that and a complete doormat to the person she obsesses over - a perfect Yandere, but Yanderes, after the bloody awesomneess do not strike me as enduring - or endearing characters. She is a slave. She has no self, other than the one that comes into existence because of another person.
I went on with the series just to see how it ended...and Yuno grew on me. Her backstory that was finally revealed actually made me pity her and make her more likeable. The Yanderes I dislike most, despite the appeal of apathy toward murder and willingness to go to extreme lengths, are the ones with no fleshed out backstory and no justified motivation, who are just kawaii killing machines. Yuno's backstory of her control-freak parents, the abuse and neglect she suffered, the breaking point of her parents' death, meant her mind would have been in a terrible and fragile state, and once her parents died, she snapped, and her shattered mind would have clung to anything to save herself - Yuki and his minute act of kindness, and hence the game by Deus to achieve Yuki. There was a method to the madness, and in an instant Yuno became a pitiful, broken girl who just wanted to be loved. A Deconstruction? Perhaps.
Overall, the plot is good, the characters believable, and action fast and gripping. But what really got me were the characters I liked and supported. And the fact that the author got me to care for a character I used to hate? What can I say? I'm impressed.