tl;dr: An interesting start that flounders due to a lack of action, lack of character development, and overtly convoluted plot. 

The manga starts off dark, mysterious, and interesting, but it sort of drops the ball after that. After the setup, things become pretty random and abrupt most of the time, pulling out random plot twists out of nowhere in a pretty rushed manner, making the plot feel overtly convoluted and actually learning the truth behind the mysteries not all that interesting. The ending itself feels like this is a series that was very obviously axed, because it just sort of stops half way through the story, and then the last scene is a flash forward to everything working out to a good ending. I appreciate that they threw in the happy ending, but it's still not all that satisfying. In terms of characters, I did like the setup of the main characters and their relationships, and the moment to moment interactions were usually amusing, but in an overarching manner they felt kind of flat and it didn't really feel like there was any development. The side characters were completely random and didn't have any value beyond the minimal impact they had in the plot. The combat system was cool at times, having the open/close mechanic and Exims with random powers to spice things up, but it was never explained properly and pretty much disappeared completely after the first major battle that seemed to start fleshing it out. The art and character designs were really good, and the blend of good looking monsters and a monstrous world worked well.