I'm not a fan of the "survival games" genre, I often find them dumb and lacking in many senses, this one on the other hand, I find quite interesting, the good intro of the MC's fallen apart life and therefore his motivation in throwing himself into a world of fighting and killing is a good intro and having a grown-up MC is a nice change, he's mature in many ways and rightly so, unlike the usual overly perfect teenager he feels more real.
What's not so great is the whole diary plot, but it's done well enough, it's the basis for justifying his fast growth and the author has foresight enough to realize and show how his own actions actually affect how the world described changed, so at least it's done properly.
Overall, it's an engaging survival game kind of story with better consistency and story-telling than most out there.