tl;dr: Interesting concepts with a pretty bad execution. 

This manga starts off with an interesting concept and some solid world building. I also thought the character designs were solid and though there weren't that many the basic character introductions were solid enough. The battle system too seemed like it had potential. However, it had a few major issues right off the bat. The first is that the pacing was pretty random. While they were still in the sanctuary it was decent enough, but after they left it felt like things got a lot more arbitrary and it didn't feel like it was telling a cohesive story. The other issue is the art, which was really rough and quite messy, so even with solid designs it wasn't nice to look at. It also feels like it got axed, resulting in everything it did build up never getting built upon and thus it never managing to get anywhere with most of what it looked like it wanted to and instead went into an ending that was rushed quite a bit, wherein the author does seem to manage to tie up every plot thread introduced so far it seems, but barely touching most of them and hence doing too much without doing anything properly.