The plot is similar to many other survivial mangas. Trapped in a place and having to solve puzzles to escape. I thought about the DS game 999 and Persona 3 a lot while reading. I thought the plot was really good and had me wondering what would happen next. However, SPOILERS AHEAD, after the gang escapes from the school I felt the whole manga took a significant drop. The story became confusing and it did not have the same suspenseful atmosphere as it did in the first half. If the manga ended when they escape I thought it would have been better. END SPOILERS
I am not great a judging art so I gave it a perfect score. I thought the settings were good and the characters were distinguishable which can be a problem with me when I'm reading manga. Everyone looks the same some times.
The characters had great personality and I would have liked to see them explored more. You learn a lot about them when you discover their powers, but then they are kinda in the background for the rest of the manga.