tl;dr: Not overtly complex or deep but solid with an interesting and well implemented art style.

This manga is one that relies primarily on its style and action. It's sense of style is certainly tremendously edgy for lack of a better word, so take that as you will, but it's really good at being so, and ultimately I thought it was really cool. The art style has a lot of grit and gore to it, but at the same time can still be quite beautiful at times, often with those elements interwoven quite tightly, which overall, I thought resulted in something that looked pretty amazing. The action was solid as well, wherein the systems weren't amazing, but they were solid, and the way it was drawn and paced was pretty exciting with scenes that were pretty awesome. In terms of the other aspects, I thought having a pretty small cast of characters that were reoccurring throughout was used well, as ultimately pretty much everyone, heroes and villains, got fleshed out to some degree. In terms of character relationships, they weren't established all that well as a whole, and while some of the smaller ones seemed fine despite that, the main ones, especially the relationship between Sayuka and Kaina felt weak. There was some growth in Sayuka, in terms of coming to do what she wanted to do, as well as in Osekami in flashbacks, in terms of her relationship with humanity, but it didn't feel particularly important in either of these cases, and the rest of the characters didn't really get much of anything. Plot wise, I think it was solid because it felt consistent from beginning to end. The plot certainly wasn't all that complex, but with the way it was told with a good portion of the story being told through flashbacks that add various twists, I think it did a good job. The ending seemed rushed, in that it forced the end to various plot threads by simply destroying them rather than resolving them, but it did deal with pretty much everything in at least some way, so all in all I was fine with where it ended so I was pretty satisfied with it. Once again, I thought the art was quite good and fit well.