I won't give a rating for this as I'm not really sure how to even begin. As far as art goes, it fits the mood of the story. The violence portrayed is certainly done with lines that suggest eroticism (in the vein of guro), so it can be extremely uncomfortable to read at time. In fact, I wish the art was a bit worse than it currently is so less of that would be going on.
The characters presented are mostly horrible caricatures of people in real life...when you first get introduced to them that is. Ryukishi has this way of introducing you to a character by presenting only one side to them and only through the story progressing does the complete picture begin to take shape. Sometimes the direction he chooses falls flat, but that only serves to make them more believable as a character imo. The same thing happens int his manga. A lot of the characters seem completely absurd, but as more and more is revealed, the larger picture is revealed and you find yourself thinking back on earlier events and looking at them in a new light.
The story is a bit confusing but as things move along, I suspect more and more will start to make sense. That's the way his stuff usually plays out, you learn one thing or think you got one thing figured out, and then you either learn more or you don't. At the very least, he usually gives enough info to piece together something that should work, which is part of the fun imo.
All in all, I think if you're a fan of his earlier works, either in VN or manga format, you should give this a try. It does feel like violence porn at times, so if you can't tolerate it, then please don't read it.
As a baseline, while never outright "hardcore" in that you can see genitalia, some of the stuff is pretty gruesome. If Tokyo Akazukin is used as a baseline for sexualized violence in a manga, then I'd say this series is about one or two notches below. The art is more suggestive than anything, and the things it manages to suggest are pretty disturbing.
That being said, if you can stomach it all and can live with being confused for most of the ride and then arriving at a horrible destination when it finishes (I'm assuming it won't be a "happy end" by most standards...but something will certainly be resolved), then I'd suggest reading it. What I said might not be the most convincing way to get people to read this series, but if all of the above applied to you in the least when it comes to finding manga to read, then you'll probably like this series. It's guaranteed to be a wild ride.