I'd say this one is really good. It takes on a new way of narrating(which might not please everyone) that gives insight into the story as if you're actually reading the MC, Rou's diary. Due to that, it's quite repetetive at times, but that makes more sence than that something new and unique would happen each and every day! I mean, most novel include long time skips, because of that limit, but since this novel is meant to resemble a diary, there'll always be an entry, even if it's sometimes really short, or really ordinary.
In that aspect, you could almost say that it reads like a Slice of Life with a bit of killing and strengthening every now and then, and the occasional eradication of a powerful foe or at times even an army.
One of it's weaknessess, except for the repetetiveness of it's format, is that some if not all of the non-monster characters, that should have a normal tempo of existence, are drawn into Rou's tempo, which contains the things other works contain in a few years in a couple of months!
Secondly, Rou's own tempo. He's a human reborn, with a (more or less) human mind! It's quite strange that he acts as if his tempo is completely normal. I mean, sure, he was probably one of the most elite humans of his time when it came to exactly tempo, but there should still be some type of 'lag', atleast the first week or two.
Thirdly, the language. The translation is done by normal people that happen to know the original language, not authors, so if you're someone that love reading stories more for the linguistic skill of the author rather than the story, this novel is not for you!
Despite these weaknesses, I'll give it a solid 8, since I'm a person that doesn't give a shit about anything but the actual story, and for the extremely interesting universe this work shows me. Still, the manga would beat this novel by far, if it wasn't for the fact that a few of the characters have been turned into some kind of comic-relief dudes, and that the release speed of the scanlated versions are bellow one chapter per month..