It had a very interesting psychological concept at its core, but it's biggest mistakes were its lack of character and story development.
I think the biggest problem in terms of character development was that they had too many characters to develop. By the end of the anime, only 3 characters out of the many established went through true character development and growth. Others were somewhat developed as well, but it seemed like it was only done as a way of explanation for another part of the story and was never revisited again.
Throughout the anime, you're given very little reason to connect with or care about the characters and whatever trouble they may be going through.
As for the story, its development seemed to take a bit of a backseat for a good part of the anime. The anime tried so hard to be mysterious that it dragged on the mystery for too long and was forced to rush to explain everything near the end. This leaves it with a lot of plot holes and senseless resolutions to several plot elements.
Overall, Mayoiga is an anime with great potential that was very badly executed.
