This is the first manga that I have felt compelled to write a review of. Some minor spoilers to follow.
First of all, a warning to everyone, the description that MAL provides is very misleading. The so called "parallel dimension" is actually a computer world.
The art is decent, I had no complaints about it, though it wasn't spectacular.
The characters however, really ruined it for me. To be quite frank, they were stupid and unbelievable. There was a lack of communication between all members of Natsuki's family, leading to the collapse of a huge computer server and thus eminent nuclear war, because one family member took the ice used to cool the computer server to preserve a corpse. Because no one told him that it could lead to the destruction of the ENTIRE WORLD. And, I'm guessing, nearly did. And another thing that I found completely unbelievable is that, with imminent nuclear destruction and annihilation of the planet, several family members were fussing more over their recently departed matriarchs funeral. Come on people, I don't know anyone who would honestly put more stock in that than the end of the world. Add to this the man who created the villain appears to be suffering from severe narcissistic personality disorder and you have a completely whacked out cast in the worst kind of way. The only ones who didn't annoy me were the main characters, Natsuki and Kenji, and Kenji's school friend Sakuma.
The premise of the story I found really annoying as well. That this computer system, OZ, controls all nuclear warheads in the WORLD, completely connects every country and is used also to control minor things like traffic lights and plumbing systems. However, not only does it control most of the world through user accounts, but it also functions as a GAME SYSTEM for bored people of the world. In addition to its world destroying capabilities if hacked. The fact that this premise is so fantastically stupid greatly annoyed me, however, once I got beyond that, the characters were also extremely annoying. I was willing to overlook one but not the other.
The manga-ka clearly did not research human behavior at all, and seemed to simply have the characters act according to how convenient it was to advance the story. And it seems like they ran out of original ideas for how to destroy the world and decided to use a game computer system that supposedly everyone in the world is on. This lack of originality and annoying premise leads me to pronounce this title a 5, I would NOT recommend it to anyone unless you enjoy reading annoying things, and the only thing that saved the rating was the decent artwork and the two main characters who I did find myself rooting for. In fact, they are the only reason that I am going to finish reading the manga at all. I could care less if OZ destroys the world.