This show is very nice on the eyes and ears. The art and animation are solid with a good use of lightning, though it does have some jarring 3D. The soundtrack is really cool and fitting and the first half has an opening and ending that I think are among some of the best ever. The acting is also good, most actors have to switch from harmless to batshit crazy and it's always believable.
Story and characters
The story and characters are rather ridiculous, though, if you apply your sense of realism to it for one second the whole thing will collapse in on itself. The way to watch Mirai Nikki is to just go with the flow, the plot is fast and full of surprises and it will keep you on the edge of your seat.
The characters are colourful and there's some nice ideas in there, but the show falls into the trap of going "see, this bad thing happened so of course they're psychopaths now!", which was really simple and nonsensical a lot of the time, like there's a primary school kid that's capable of elaborate maniacal murder. The lead is another one of those whiny anime protagonists, whose big tragedy is that his parents are divorced and now he doesn't have a perfect family, but really who cares this is the anime that has Yuno in it. For those who aren't in on it, Yuno is the most yanderest yandere that has ever picked up a cleaver for the dude she loves and she is terrible and impossible to hate. A lot of the time she's basically the perfect girlfriend and completely devoted to Yuki, except she's also murderous and obsessive and all round crazy as hell. Yuki uses her devotion but gets so wrapped up in his act and Yuno's possessive declarations of love that he starts to fall for her and that is some psychological horror right there except I think we're supposed to think it's positive by the end. Eh.
There are a lot more characters but I can't go into the entire cast, I will just briefly highlight that there's a Kaworu ripoff for the slash shippers and that I think the most likeable character is the terrorist that blew up half of Yuki's school while there were people in it. It's that kind of show.
Final thoughts
I watched this show when I was sick and just wanted to see things get killed, it is absolutely great for that. I could write for ages about why this show is disturbing, nonsensical and wrong, but if you just take it for what it is and enjoy the plot it's very entertaining.
